Code review comment for lp:~widelands-dev/widelands/bug-1489295-mine-is-exhausted

The empty string check is necessary for buildings with an empty out_of_resource_heading. If we don't check for an empty string, the message "Did not start scouting because Ration is missing" for scouts will never show up, maybe other buildings will have missing tooltips as well (e.g. tavern/inn), if we don't check.

I did it the "complicated" way because I found it to be easier to read. And for log output (has to be removed later on though)