Global: Cleanup initialization/pointer checks.

Cleaning up a lot of cases of uninitialized data, unchecked return values
for failures, and similar.

Windows/DSoundStream.cpp

@@ -183,6 +183,8 @@ bool DSoundAudioBackend::Init(HWND window, StreamCallback _callback, int sampleR
 	sampleRate_ = sampleRate;
 	threadData_ = 0;
 	hThread_ = (HANDLE)_beginthreadex(0, 0, soundThread, (void *)this, 0, 0);
+	if (!hThread_)
+		return false;
 	SetThreadPriority(hThread_, THREAD_PRIORITY_ABOVE_NORMAL);
 	return true;
 }