Fix a crash in the linear resampler when LPF order is 0.

Public issue https://github.com/dr-soft/miniaudio/issues/155

miniaudio.h

@@ -5160,6 +5160,11 @@ Calculates a buffer size in frames from the specified number of milliseconds and
 */
 MA_API ma_uint32 ma_calculate_buffer_size_in_frames_from_milliseconds(ma_uint32 bufferSizeInMilliseconds, ma_uint32 sampleRate);
 
+/*
+Copies PCM frames from one buffer to another.
+*/
+MA_API void ma_copy_pcm_frames(void* dst, const void* src, ma_uint64 frameCount, ma_format format, ma_uint32 channels);
+
 /*
 Copies silent frames into the given buffer.
 */
@@ -8840,6 +8845,11 @@ MA_API ma_uint32 ma_calculate_buffer_size_in_frames_from_milliseconds(ma_uint32
     return bufferSizeInMilliseconds * (sampleRate/1000); 
 }
 
+MA_API void ma_copy_pcm_frames(void* dst, const void* src, ma_uint64 frameCount, ma_format format, ma_uint32 channels)
+{
+    ma_copy_memory_64(dst, src, frameCount * ma_get_bytes_per_frame(format, channels));
+}
+
 MA_API void ma_zero_pcm_frames(void* p, ma_uint64 frameCount, ma_format format, ma_uint32 channels)
 {
     ma_zero_memory_64(p, frameCount * ma_get_bytes_per_frame(format, channels));
@@ -32759,7 +32769,11 @@ MA_API ma_linear_resampler_config ma_linear_resampler_config_init(ma_format form
 
 static ma_result ma_linear_resampler_set_rate_internal(ma_linear_resampler* pResampler, ma_uint32 sampleRateIn, ma_uint32 sampleRateOut, ma_bool32 isResamplerAlreadyInitialized)
 {
+    ma_result result;
     ma_uint32 gcf;
+    ma_uint32 lpfSampleRate;
+    double lpfCutoffFrequency;
+    ma_lpf_config lpfConfig;
 
     if (pResampler == NULL) {
         return MA_INVALID_ARGS;
@@ -32777,34 +32791,28 @@ static ma_result ma_linear_resampler_set_rate_internal(ma_linear_resampler* pRes
     pResampler->config.sampleRateIn  /= gcf;
     pResampler->config.sampleRateOut /= gcf;
 
-    if (pResampler->config.lpfOrder > 0) {
-        ma_result result;
-        ma_uint32 lpfSampleRate;
-        double lpfCutoffFrequency;
-        ma_lpf_config lpfConfig;
-
-        if (pResampler->config.lpfOrder > MA_MAX_FILTER_ORDER) {
-            return MA_INVALID_ARGS;
-        }
+    /* Always initialize the low-pass filter, even when the order is 0. */
+    if (pResampler->config.lpfOrder > MA_MAX_FILTER_ORDER) {
+        return MA_INVALID_ARGS;
+    }
 
-        lpfSampleRate      = (ma_uint32)(ma_max(pResampler->config.sampleRateIn, pResampler->config.sampleRateOut));
-        lpfCutoffFrequency = (   double)(ma_min(pResampler->config.sampleRateIn, pResampler->config.sampleRateOut) * 0.5 * pResampler->config.lpfNyquistFactor);
+    lpfSampleRate      = (ma_uint32)(ma_max(pResampler->config.sampleRateIn, pResampler->config.sampleRateOut));
+    lpfCutoffFrequency = (   double)(ma_min(pResampler->config.sampleRateIn, pResampler->config.sampleRateOut) * 0.5 * pResampler->config.lpfNyquistFactor);
 
-        lpfConfig = ma_lpf_config_init(pResampler->config.format, pResampler->config.channels, lpfSampleRate, lpfCutoffFrequency, pResampler->config.lpfOrder);
+    lpfConfig = ma_lpf_config_init(pResampler->config.format, pResampler->config.channels, lpfSampleRate, lpfCutoffFrequency, pResampler->config.lpfOrder);
 
-        /*
-        If the resampler is alreay initialized we don't want to do a fresh initialization of the low-pass filter because it will result in the cached frames
-        getting cleared. Instead we re-initialize the filter which will maintain any cached frames.
-        */
-        if (isResamplerAlreadyInitialized) {
-            result = ma_lpf_reinit(&lpfConfig, &pResampler->lpf);
-        } else {
-            result = ma_lpf_init(&lpfConfig, &pResampler->lpf);
-        }
+    /*
+    If the resampler is alreay initialized we don't want to do a fresh initialization of the low-pass filter because it will result in the cached frames
+    getting cleared. Instead we re-initialize the filter which will maintain any cached frames.
+    */
+    if (isResamplerAlreadyInitialized) {
+        result = ma_lpf_reinit(&lpfConfig, &pResampler->lpf);
+    } else {
+        result = ma_lpf_init(&lpfConfig, &pResampler->lpf);
+    }
 
-        if (result != MA_SUCCESS) {
-            return result;
-        }
+    if (result != MA_SUCCESS) {
+        return result;
     }
 
     pResampler->inAdvanceInt  = pResampler->config.sampleRateIn / pResampler->config.sampleRateOut;
@@ -42484,10 +42492,12 @@ REVISION HISTORY
 ================
 v0.10.5 - TBD
   - Change ma_zero_pcm_frames() to take a 64-bit frame count.
+  - Add ma_copy_pcm_frames().
   - Add MA_NO_GENERATION build option to exclude the `ma_waveform` and `ma_noise` APIs from the build.
   - Add support for formatted logging to the VC6 build.
-  - Minor documentation updates.
+  - Fix a crash in the linear resampler when LPF order is 0.
   - Fix compilation errors and warnings with older versions of Visual Studio.
+  - Minor documentation updates.
 
 v0.10.4 - 2020-04-12
   - Fix a data conversion bug when converting from the client format to the native device format.