Silence LoadError only if it is for rubygems itself

[intuxicated]

Background

#2764 attempted to prevent raising LoadError when requiring rubygems because it might not be available optionally when Ruby is delivered via packaging systems and instead prints a warning message.

Context

I was working on a feature in RubyGems to better communicate to users that something went wrong when loading rubygems/defaults/operating_system and after writing a test, I saw that any LoadError exception raised by the rubygems will be captured and a warning will be printed instead (rubygems/rubygems#4824). Although #2764 intention was to prevent failure when 'rubygems' are not available, it's capturing every LoadError that might happen inside the rubygems at runtime.

Change

Prevent raising the LoadError exception only if it's related directly to loading rubygems.