Memory Access Violation on SANE's test backend

[goncalomb]

During the sane-wasm build we are suppose to set number_of_devices to 0 (test backend). But I've discovered an issue with that option, see build.sh comment:

https://github.com/goncalomb/sane-wasm/blob/3100bc98c037cd8ff63ea19c8dd98e3f13931b2f/build.sh#L236-L251

The issue is most likely on the file backends/backend/test.c.

The backends patch should be updated to include the fix: https://github.com/goncalomb/sane-wasm/tree/master/deps. And bonus points for fixing it upstream: https://gitlab.com/sane-project/backends/-/issues.