Update #4 - minor fixes

Hi everyone,

two minor fixes were made:

• rendering of purple circle, showing range is in sync if UPGRADE button is disabled

• fix for not unlocking next mission in case previous mission was solved

Also, additional note about mission unlocking mechanism.

First mission unlocks 2nd mission while 2nd mission unlocks 3rd mission on current station AND 1st mission on next station.

Vedran Klanac, creator of Solar Division