SANE genesys backend causes lockup during sane_get_devices

[goncalomb]

The genesys backend (http://www.sane-project.org/sane-backends.html#S-GENESYS) is used by a fair number of devices, so it would be good to find the issue that is causing it to lock during sane_get_devices, and re-enable the backend.

https://github.com/goncalomb/sane-wasm/blob/2d1148196c42f2df188912fab5cb4c9cf16295dc/build.sh#L126-L136

Can be debugged using the test page, by stopping script execution right after sane_get_devices. But can cause the inspector to lock and crash.