renderer: catch shader source processing exceptions and print raw source

[illwieckz]

Catch shader source processing exceptions and print raw source if something bad happened while processing the source.

See #1612:

• https://github.com/DaemonEngine/Daemon/issues/1612

This doesn't fix the underlying cause of the processing error, but at least the engine doesn't crash, the source get printed, the error message get printed, and it is possible to debug the GLSL shader code in some kind of degraded mode.

[slipher]

I think we should just fix the text processing code. That code is a good candidate for unit testing.