WASAPI: Fix an error with device enumeration.

There are two problems with this:

 * The pInfo buffer is being accessed when set to NULL
 * The count is not getting set correctly when pInfo = NULL

mini_al.h

@@ -3076,7 +3076,9 @@ static mal_result mal_enumerate_devices__wasapi(mal_context* pContext, mal_devic
         return mal_context_post_error(pContext, NULL, "[WASAPI] Failed to get device count.", MAL_NO_DEVICE);
     }
 
-    for (mal_uint32 iDevice = 0; iDevice < infoSize && iDevice < count; ++iDevice) {
+    for (mal_uint32 iDevice = 0; iDevice < count; ++iDevice) {
+        if (pInfo != NULL) {
+            if (infoSize > 0) {
                 mal_zero_object(pInfo);
 
                 IMMDevice* pDevice;
@@ -3116,8 +3118,13 @@ static mal_result mal_enumerate_devices__wasapi(mal_context* pContext, mal_devic
                 }
 
                 pInfo += 1;
+                infoSize -= 1;
                 *pCount += 1;
             }
+        } else {
+            *pCount += 1;
+        }
+    }
 
     IMMDeviceCollection_Release(pDeviceCollection);
 #else
@@ -10217,6 +10224,7 @@ void mal_pcm_f32_to_s32(int* pOut, const float* pIn, unsigned int count)
 //     which is by design.
 //   - ALSA: Add support for excluding the "null" device using the alsa.excludeNullDevice context config variable.
 //   - ALSA: Fix a bug with channel mapping which causes an assertion to fail.
+//   - WASAPI: Fix device enumeration when passing NULL to the pInfo parameter.
 //
 // v0.4 - 2017-11-05
 //   - API CHANGE: The log callback is now per-context rather than per-device and as is thus now passed to