Fix use of uninitialized variables

When shutting down, the resultALSA variable can be used when
uninitialized in the ma_device_read__alsa and ma_device_write__alsa
routines.  This has been verified by both gcc warnings and in
application code (we were occasionally seeing segfaults when our
callback routine was being passed a crazy large value for the number of
frames read when shutting down).
Signed-off-by: Charles Steinkuehler <charles@steinkuehler.net>

miniaudio.h

@@ -21213,7 +21213,7 @@ static ma_result ma_device_wait_write__alsa(ma_device* pDevice)
 
 static ma_result ma_device_read__alsa(ma_device* pDevice, void* pFramesOut, ma_uint32 frameCount, ma_uint32* pFramesRead)
 {
-    ma_snd_pcm_sframes_t resultALSA;
+    ma_snd_pcm_sframes_t resultALSA = 0;
 
     MA_ASSERT(pDevice != NULL);
     MA_ASSERT(pFramesOut != NULL);
@@ -21267,7 +21267,7 @@ static ma_result ma_device_read__alsa(ma_device* pDevice, void* pFramesOut, ma_u
 
 static ma_result ma_device_write__alsa(ma_device* pDevice, const void* pFrames, ma_uint32 frameCount, ma_uint32* pFramesWritten)
 {
-    ma_snd_pcm_sframes_t resultALSA;
+    ma_snd_pcm_sframes_t resultALSA = 0;
 
     MA_ASSERT(pDevice != NULL);
     MA_ASSERT(pFrames != NULL);