mmsystem: Use PeekMessageW instead of UserYield.

dlls/mmsystem.dll16/mci16.c

@@ -482,7 +482,8 @@ static UINT MCI_Yield1632(DWORD pfn16, MCIDEVICEID id, DWORD yield_data)
 
     if (!pfn16)
     {
-        UserYield16();
+        MSG msg;
+        PeekMessageW( &msg, 0, 0, 0, PM_REMOVE | PM_QS_SENDMESSAGE );
         return 0;
     }
 

dlls/mmsystem.dll16/mmsystem.c

@@ -2059,7 +2059,8 @@ LRESULT	WINAPI mmThreadCreate16(FARPROC16 fpThreadAddr, LPHANDLE16 lpHndl, DWORD
 		WARN("Couldn't resume thread\n");
 
 	    while (lpMMThd->dwStatus != 0x10) { /* test also HIWORD of dwStatus */
-		UserYield16();
+                MSG msg;
+                PeekMessageW( &msg, 0, 0, 0, PM_REMOVE | PM_QS_SENDMESSAGE );
 	    }
 	}
     }