sceUsbMic: Don't crash when there's no Windows capture device object

Only the app creates winMic, so a blocking mic read crashed headless.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

Core/HLE/sceUsbMic.cpp

@@ -346,7 +346,8 @@ int Microphone::stopMic() {
 
 bool Microphone::isHaveDevice() {
 #ifdef HAVE_WIN32_MICROPHONE
-	return winMic->getDeviceCounts() >= 1;
+	// Only the app creates winMic, headless doesn't.
+	return winMic && winMic->getDeviceCounts() >= 1;
 #elif PPSSPP_PLATFORM(ANDROID)
 	return System_AudioRecordingIsAvailable();
 #endif