Fixing the logic of rising exceptions when iterating through the stores

[v-yadli]

In the original logic, when seeking for a match through the stores of ri docs (system, gems, ...), if there is an exception (which will occur when one of the store failed to load a klass), the whole procedure is interrupted.

Since system is put before gem, all goods in the gem store are actually not approachable.

This commit fixes (not sure if completely) this issue.

[danchoi]

Thank you

[v-yadli]

I'm glad that I can do some help. Getting more familiar with ruby now :-)