Fix a bug with ma_vfs_read().

This is not pre-initializing the variable that receives the number of
bytes read to 0 which can result in custom VFS implementations
returning an invalid value if they return early from an error or
whatnot.

miniaudio.h

@@ -58510,7 +58510,7 @@ MA_API ma_result ma_vfs_read(ma_vfs* pVFS, ma_vfs_file file, void* pDst, size_t
 {
     ma_vfs_callbacks* pCallbacks = (ma_vfs_callbacks*)pVFS;
     ma_result result;
-    size_t bytesRead;
+    size_t bytesRead = 0;
 
     if (pBytesRead != NULL) {
         *pBytesRead = 0;