Fix for issue #178

When doing G_RunThink for NPCs, it will skip the NPC_Think function and only run icarus when it hasn't reached the nextthink time.
Which means that the NPCGlobals such as NPCInfo will not be set for this run of icarus.
This causes null pointer crashes when icarus needs to access the npc globals.
Merge pull request #183 from xScooper/master

Fix for issue #178