Synchronous Audio Router crashes when the "Configure" button is clicked

[dechamps]

When FlexASIO is selected as the backend of Synchronous Audio Router 0.13.1, if the "Configure" button is clicked in SAR, the process crashes.

Further investigation reveals that when the button is clicked, SAR initializes a second instance of FlexASIO inside the same process, without closing the first one beforehand. This is arguably a misuse of the ASIO API, which does not really allow for multiple ASIO driver instances inside a single process. (Nevertheless, it might be prudent, perhaps even useful, to make FlexASIO more tolerant to being instantiated multiple times.)

The crash occurs on this line, which is not surprising given this->write is a global variable:

FlexASIO/src/flexasio/FlexASIOUtil/portaudio.cpp

Lines 43 to 44 in 57e14e8

	if (this->write) abort();
	this->write = std::move(write);

[dechamps]

I filed eiz/SynchronousAudioRouter#133 to suggest to the SAR folks that they might want to stop doing this as (IMHO) it is not compliant with the ASIO spec and might cause problems with other drivers besides FlexASIO.

[dechamps]

This is fixed in FlexASIO 1.10, which now allows multiple FlexASIO instances to exist simultaneously in the same process.