winmm: Buffer size must be at least MMIO_DEFAULTBUFFER (8192) bytes.

mmioOpen() with the length of buffer set to 0 expects the buffer to be at least
MMIO_DEFAULTBUFFER (8192) bytes in size, and using buffer of smaller size can
lead to various problems when the buffer actually gets used.

dlls/winmm/tests/mmio.c

@@ -199,7 +199,7 @@ static void test_mmioDescend(char *fname)
 
 static void test_mmioOpen(char *fname)
 {
-    char buf[256];
+    char buf[MMIO_DEFAULTBUFFER];
     MMRESULT ret;
     HMMIO hmmio;
     MMIOINFO mmio;