OpenCS: Attribute and Skill can be selected for spells that do not require these parameters, leading to non-functional spells

Example:

1. Create a spell in OpenCS with Sound for 5 seconds on self, 5 duration
2. Add Block under Skill and Strength under Attribute to the Sound effect.
3. Use spell in game: it does nothing, including no sound effect

More info:

This doesn't occur in the above example unless both a Skill and an Attribute are selected. However, I had another case where a spell with only an accidental Skill entry caused the game to "pause" i.e. the gameworld to be frozen, but the menus could still be accessed. Unfortunately I didn't save the spell parameters and I can't reproduce this effect.

(RM-2980 from redmine: created on 2015-10-27 by Zeo fig, , closed on 2015-10-29 by cc 9cii)