Resolve assertion when CollectorNomad2 dies

It is possible to cause the death of the CollectorNomad2 object (rush
to it before it possibly leaves again into the sidepackets the ship
won't fit through). The transition happens here:

```
f0  KillObject (objp=0x3d4d3e0 <Objects+384000>, killer=0x3cef7e0 <Objects>, damage=3) at /home/jengelh/D3/Descent3/damage.cpp:1036
f1  ApplyDamageToGeneric (hit_obj=0x3d4d3e0 <Objects+384000>, killer=0x3cef7e0 <Objects>, damage_type=6, damage=3, server_says=0, weapon_id=255) at /home/jengelh/D3/Descent3/damage.cpp:1401
f2  collide_generic_and_player (robotobj=0x3d4d3e0 <Objects+384000>, playerobj=0x3cef7e0 <Objects>, collision_point=0x7f877f40a830, collision_normal=0x7f877f40a858, f_reverse_normal=true, hit_info=0x7f877f40a810) at /home/jengelh/D3/physics/collide.cpp:2127
f3  collide_two_objects (A=0x3cef7e0 <Objects>, B=0x3d4d3e0 <Objects+384000>, collision_point=0x7f877f40a830, collision_normal=0x7f877f40a858, hit_info=0x7f877f40a810) at /home/jengelh/D3/physics/collide.cpp:2505
f4  do_physics_sim (obj=0x3cef7e0 <Objects>) at /home/jengelh/D3/physics/physics.cpp:1515
f5  ObjDoFrame (obj=0x3cef7e0 <Objects>) at /home/jengelh/D3/Descent3/object.cpp:2824
f6  ObjDoFrameAll () at /home/jengelh/D3/Descent3/object.cpp:2988
f7  GameFrame () at /home/jengelh/D3/Descent3/GameLoop.cpp:2980
f8  GameSequencer () at /home/jengelh/D3/Descent3/gamesequence.cpp:1221
f9  PlayGame () at /home/jengelh/D3/Descent3/game.cpp:834
f10 MainLoop () at /home/jengelh/D3/Descent3/descent.cpp:550
f11 Descent3 () at /home/jengelh/D3/Descent3/descent.cpp:508
f12 oeD3LnxApp::run (this=0x7f877f00db50) at /home/jengelh/D3/Descent3/sdlmain.cpp:151

<frame 2> (gdb) p robotobj
$1 = {
	type = 2 '\002' (OBJ_ROBOT), dummy_type = 255 '\377', id = 276,
	flags = 2135072, name = 0x5020000aff30 "CollectorNomad2",
	handle = 2432, next = 178, prev = -1,
	control_type = 1 '\001' (CT_AI), movement_type = 2 '\002' (MC_ROLLING),
	render_type = 1 '\001' (LRT_GOURAUD), lighting_render_type = 1 '\001', roomnum = 58,
	pos = {x = 2350.21484, y = -263.523956, z = 1868.59888},
	orient = {
		rvec = {x = 0.882905424, y = 1.63964216e-14, z = -0.469550878},
		uvec = {x = -1.25793295e-14, y = 1, z = 1.12662192e-14},
		fvec = {x = 0.469550878, y = -4.04037088e-15, z = 0.882905424}
	},...}
```

Thus, KillObject sets obj->control_type=CT_DYING. In the same game
tick, Level6.cpp then calls aAIGoalFollowPathSimple which triggers
the assertion.

```
Int3 in $GIT/Descent3/osiris_predefs.cpp at line 571.(Descent 3 Debug Break)

f0  osipf_AIGoalFollowPathSimple (objhandle=2432, path_id=21, guid=7, flags=1052928, slot=3) at $GIT/Descent3/osiris_predefs.cpp:571
f1  AI_GoalFollowPathSimple (objhandle=2432, path_id=21, guid=7, flags=1052928, slot=3) at $GIT/scripts/osiris_import.h:170
f2  aAIGoalFollowPathSimple (objhandle=2432, pathid=21, flags=1052928, goalid=7, priority=3) at $GIT/scripts/DallasFuncs.cpp:3649
f3  LevelScript_0000::CallEvent (this=0x5020000ba430, event=256, data=0x7f963e71d930) at $GIT/scripts/Level6.cpp:2465
f4  CallInstanceEvent (id=0, ptr=0x5020000ba430, event=256, data=0x7f963e71d930) at $GIT/scripts/Level6.cpp:2209
f5  Osiris_CallLevelEvent (event=256, data=0x7f963e71d930) at $GIT/Descent3/OsirisLoadandBind.cpp:2000
f6  GameFrame () at $GIT/Descent3/GameLoop.cpp:3020
f7  GameSequencer () at $GIT/Descent3/gamesequence.cpp:1221
f8  PlayGame () at $GIT/Descent3/game.cpp:834
f9  MainLoop () at $GIT/Descent3/descent.cpp:550
f10 Descent3 () at $GIT/Descent3/descent.cpp:508
f11 oeD3LnxApp::run (this=0x7f963e80db50) at $GIT/Descent3/sdlmain.cpp:151
```

scripts/Level6.cpp

@@ -1553,6 +1553,7 @@ const char *Object_names[NUM_OBJECT_NAMES] = {"DummyFlag",
                                         "BuilderPuzzUFO1",
                                         "BuilderPuzzUFO2",
                                         "BuilderPuzzUFO3",
+                                        // Spelling mistake is what it is (forced by d3_2.mn3 contents)
                                         "CollectorNomad2",
                                         "CollectorsNomad1",
                                         "VolcanoSpew",