fix(plugins): Stops junk log entries created on plugins page

If a plugin's directory was removed, viewing the plugins page results
in this plugin being re-disabled again and again, adding junk log
entries. Now we only disable if the plugin wasn't already disabled.

Fixes #6066
Merge pull request #6351 from mrclay/6066

fix(plugins): Stops junk log entries created on plugins page

If a plugin's directory was removed, viewing the plugins page results
in this plugin being re-disabled again and again, adding junk log
entries. Now we only disable if the plugin wasn't already disabled.