cast uniform location to uint32_t

[watasuke102]

Context

Currently build fails by the following error:

/home/watasuke/program/zwin/zen-remote/src/client/gl-base-technique.cc:145:58: error: non-constant-expression cannot be narrowed from type 'int32_t' (aka 'int') to 'unsigned int' in initializer list [-Wc++11-narrowing-const-reference]
  145 |                     std::pair<uint32_t, UniformVariable>{location, {}});
      |                                                          ^~~~~~~~

Summary

cast location to uint32_t; location is positive number on this (changed) line, so casting is safe

How to check the behavior

Build succeeds without errors