[core] Better error message is proto is invalid.

[ChrisCummins]

No description provided.

[codecov-commenter]

Codecov Report

Merging #628 (b4217a9) into development (c5b9289) will decrease coverage by 0.12%.
The diff coverage is 60.00%.

@@               Coverage Diff               @@
##           development     #628      +/-   ##
===============================================
- Coverage        88.75%   88.63%   -0.13%     
===============================================
  Files              115      115              
  Lines             7019     7024       +5     
===============================================
- Hits              6230     6226       -4     
- Misses             789      798       +9     

Impacted Files	Coverage Δ
compiler_gym/views/observation_space_spec.py	84.84% <60.00%> (-4.44%)	⬇️
compiler_gym/envs/llvm/datasets/cbench.py	79.42% <0.00%> (-1.09%)	⬇️
...loop_tool/service/loop_tool_compilation_session.py	89.79% <0.00%> (-0.69%)	⬇️
compiler_gym/envs/compiler_env.py	91.85% <0.00%> (-0.50%)	⬇️
compiler_gym/envs/gcc/service/gcc_service.py	96.70% <0.00%> (-0.37%)	⬇️

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