libretro: Increase size of allocated audio buffer

- It turns out that because the nominal size divided by number of channels is an odd number,
  potator can write past the end of the buffer when fetching samples. We therefore need
  additional padding. Note that this error is not detected by ASAN under Linux (!)

platform/libretro/libretro.c

@@ -477,7 +477,11 @@ void retro_init(void)
    video_buffer = (uint8_t*)malloc(VIDEO_BUFFER_SIZE * sizeof(uint8_t));
 #endif
 
-   audio_buffer = (int16_t*)malloc(AUDIO_BUFFER_SIZE * sizeof(int16_t));
+   /* Round up actual size to nearest multiple of 128
+    * > Since (AUDIO_BUFFER_SIZE / 2) is an odd number,
+    *   potator can write past the end of the buffer,
+    *   so we need some extra padding... */
+   audio_buffer = (int16_t*)malloc(((AUDIO_BUFFER_SIZE + 0x7F) & ~0x7F) * sizeof(int16_t));
 }
 
 void retro_deinit(void)