(glslang_validator): don't run the command when there are no glsl files
What does this MR do?
- Prevent sheldon from crashing when glslangValidator is not found and no glsl files were edited.
- Fix the error message when glslangValidator is not found.
- Fix the crash when no version is defined.
How to test it?
See steps in !9 (merged)
Associated Issues/Merge Requests
Fixes #11 (closed)
Edited by Kevin GAUDET