Calling getExtension with empty string results in exception

When calling glbinding::aux::Meta::getExtension(const std::string & extension) with an empty string an exception is thrown as the function attempts to access the string at a specific index unchecked when trying to skip the prefix.

See:
https://github.com/cginternals/glbinding/blob/69e75ea4907933ba302eeb5fd6f95495210f2f30/source/glbinding-aux/source/Meta.cpp#L97

https://github.com/cginternals/glbinding/blob/69e75ea4907933ba302eeb5fd6f95495210f2f30/source/glbinding-aux/source/Meta.cpp#L49

Start in source/glbinding-aux/source/Meta.cpp at the referenced lines in getExtension and the prefix-skipping logic. Reproduce the issue with an empty extension string, then inspect the existing tests or test setup for Meta. Done means calling getExtension with an empty string no longer throws an exception and the relevant test passes.

Written by the indexing model from the issue text.