Assert may not have been a NOOP

[philburk]

In a review of a WASAPI change I stated that an assert was a NOOP.

Originally posted by @philburk in #948 (comment)

But after rereading the code I realize that I misread line 1425. I thought it was checking "subtream->monoBuffer". But it was checking "subtream->monoMixer". So the assert(subtream->monoBuffer != NULL) actually did something.

If Dmitry wants to add it back in that is fine with me.

[dmitrykos]

I replaced this assert with a new one to assert the reason rather than consequence to assist the understanding of the logic:

portaudio/src/hostapi/wasapi/pa_win_wasapi.c

Line 1432 in c121482

assert(subStream->wavexu.ext.Format.nBlockAlign != 0);

subtream->monoBuffer can become NULL in that piece of logic only if this condition fails when monoBufferSize is 0 because initially subStream->monoBufferSize is 0 and it is set only inside this function when monoBuffer is allocated successfully:

portaudio/src/hostapi/wasapi/pa_win_wasapi.c

Lines 1435 to 1436 in c121482

	UINT32 monoBufferSize = frames * subStream->wavexu.ext.Format.nBlockAlign;
	if (monoBufferSize > subStream->monoBufferSize)

but it will not happen if frames and nBlockAlign are not 0. So for now I think assert(subtream->monoBuffer != NULL) is no longer needed.