winmm: Fix MEVT_LONGMSG handling in MIDI stream.

dlls/winmm/tests/midi.c

@@ -819,7 +819,7 @@ static void test_midiStream(UINT udev, HWND hwnd)
         e->dwEvent = MEVT_F_LONG | sizeof(SysEx_volume_off);
         memcpy(&e->dwParms[0], SysEx_volume_off, sizeof(SysEx_volume_off));
         p += sizeof(MIDISHORTEVENT) + ROUNDUP4(sizeof(SysEx_volume_off));
-        /* Note On (FIXME: we shouldn't hear this voice due to volume settings) */
+        /* Note On (We can't hear this voice due to volume settings) */
         e = (MIDIEVENT *)p;
         e->dwEvent = MEVT_F_SHORT | 0x6F4593; /* note #69 */
         p += sizeof(MIDISHORTEVENT);

dlls/winmm/winmm.c

@@ -1169,8 +1169,16 @@ start_header:
 	    /* do nothing, skip bytes */
 	    break;
 	case MEVT_LONGMSG:
-	    midiOutLongMsg(lpMidiStrm->hDevice, lpMidiStrm->lpMidiHdr, MEVT_EVENTPARM(me->dwEvent));
-	    break;
+        {
+            MIDIHDR mh;
+            memset(&mh, 0, sizeof(mh));
+            mh.lpData = (LPSTR)me->dwParms;
+            mh.dwBufferLength = MEVT_EVENTPARM(me->dwEvent);
+            midiOutPrepareHeader(lpMidiStrm->hDevice, &mh, sizeof(mh));
+            midiOutLongMsg(lpMidiStrm->hDevice, &mh, sizeof(mh));
+            midiOutUnprepareHeader(lpMidiStrm->hDevice, &mh, sizeof(mh));
+            break;
+        }
 	case MEVT_NOP:
 	    break;
 	case MEVT_SHORTMSG: