Improved error reporting for missing / incorrect shader

[mvaligursky]

• when a shader (vertex or fragment) is not specified, we print error to console, and avoid crash when reporting the line number later.
• when shader failed to compile, we skip over rendering meshes that use it to avoid flood of unrelated errors.

based on an issue reported here https://forum.playcanvas.com/t/declaration-variables-in-shaders/20906/3

[Maksims]

Awesome!
Also, would love to have better reporting of error code, instead of the whole shader, just perhaps 3 lines before and 3 lines after with line numbers - would be great. Otherwise, it is a lot of scrolling.

Also, please take into account a scenario where material chunks are re-applied and the shader is queued for recompile, which can lead to fixing or error (again). This workflow is really useful when writing shaders with live-reload by subscribing to the asset load event.

[mvaligursky]

Good suggestion @Maksims - I get annoying by those long shaders in the errors as well. I'll create a separate issue to address.

The recompiling part should work - I believe you fixed it many months ago, and that should still work.

[mvaligursky]

@Maksims - issue created #3280