Fix #20907 - Regardless of check code in a plugin, starting a plugin with no score open crashes the program.

A diagnostic "prinf" statement was unconditionally trying to access the score name, even with no score. Corrected by adding a condition.
Merge pull request #329 from mgavioli/Fix_20907_plugin_no-score_crash

Fix #20907 - Crash when starting a plugin with no score open