Set active collision group in FishHarmless::initialize()

Previously, only the current collision group was set on initialization, which caused re-activating the fish to have its collision group set to a different one.

This issue is now fixed, by setting the active collision group on initialization as well.

src/badguy/fish_harmless.cpp

@@ -26,7 +26,7 @@ void
 FishHarmless::initialize()
 {
   FishSwimming::initialize();
-  set_group(COLGROUP_MOVING_ONLY_STATIC);
+  set_colgroup_active(COLGROUP_MOVING_ONLY_STATIC);
 }
 
 /* EOF */