coreaudio: Make sure Port_SendToMessageThread is not NULL before calling CFMessagePortSendRequest.

dlls/winecoreaudio.drv/audio.c

@@ -349,6 +349,9 @@ static void wodSendNotifyCompletionsMessage(WINE_WAVEOUT* wwo)
     CFDataRef data;
     UInt32 buffer;
 
+    if (!Port_SendToMessageThread)
+        return;
+
     buffer = (UInt32) wwo->woID;
 
     data = CFDataCreate(kCFAllocatorDefault, (UInt8 *)&buffer, sizeof(buffer));
@@ -368,6 +371,9 @@ static void wodSendNotifyInputCompletionsMessage(WINE_WAVEIN* wwi)
     CFDataRef data;
     UInt32 buffer;
 
+    if (!Port_SendToMessageThread)
+        return;
+
     buffer = (UInt32) wwi->wiID;
 
     data = CFDataCreate(kCFAllocatorDefault, (UInt8 *)&buffer, sizeof(buffer));
@@ -694,6 +700,9 @@ void CoreAudio_WaveRelease(void)
     /* Stop CFRunLoop in messageThread */
     TRACE("()\n");
 
+    if (!Port_SendToMessageThread)
+        return;
+
     CFMessagePortSendRequest(Port_SendToMessageThread, kStopLoopMessage, NULL, 0.0, 0.0, NULL, NULL);
     CFRelease(Port_SendToMessageThread);
     Port_SendToMessageThread = NULL;