matdbg crashes when editing featureLevel: 0 materials on a FEATURE_LEVEL_0 device

[pixelflinger]

This is happening because matdbg doesn't understand the Essl1 chunk and we end-up replacing the wrong one, but there are probably other issues; it seems that it's also not selecting the right compilation options.

This can be reproduced with the helloTriangle sample in the emulator by using the config.forceGLES2Context option, or using a real ES2 device.