Make MMIO_Open work with NULL filename again.

dlls/winmm/mmio.c

@@ -509,6 +509,8 @@ static FOURCC MMIO_ParseExt(LPCSTR szFileName)
     
     TRACE("(%s)\n",debugstr_a(szFileName));
     
+    if (!szFileName)
+	return ret;
     extEnd = strrchr(szFileName,'+');
     if (extEnd) {
 	/* Need to parse to find the extension */
@@ -734,7 +736,7 @@ static HMMIO MMIO_Open(LPSTR szFileName, MMIOINFO* refmminfo,
     if ((wm = MMIO_Create()) == NULL)
 	return 0;
 
-    /* If both params are NULL, then parse the file name */
+    /* If both params are NULL, then parse the file name if available */
     if (refmminfo->fccIOProc == 0 && refmminfo->pIOProc == NULL) {
 	wm->info.fccIOProc = MMIO_ParseExt(szFileName);
 	/* Handle any unhandled/error case. Assume DOS file */