SL-20714 Crash accessing mControlAVBridge

Looks like control avatar was recreated after cleanup then object was
deleted

indra/newview/llviewermessage.cpp

@@ -4229,7 +4229,7 @@ void process_object_animation(LLMessageSystem *mesgsys, void **user_data)
     LLObjectSignaledAnimationMap::instance().getMap()[uuid] = signaled_anims;
     
     LLViewerObject *objp = gObjectList.findObject(uuid);
-    if (!objp)
+    if (!objp || objp->isDead())
     {
 		LL_DEBUGS("AnimatedObjectsNotify") << "Received animation state for unknown object " << uuid << LL_ENDL;
         return;

indra/newview/llviewerobject.cpp

@@ -391,6 +391,7 @@ LLViewerObject::~LLViewerObject()
 	sNumObjects--;
 	sNumZombieObjects--;
 	llassert(mChildList.size() == 0);
+    llassert(mControlAvatar.isNull()); // Should have been cleaned by now
 
 	clearInventoryListeners();
 }
@@ -3106,6 +3107,10 @@ void LLViewerObject::updateControlAvatar()
         return;
     }
 
+    // caller isn't supposed to operate on a dead object,
+    // avatar was already cleaned up
+    llassert(!isDead());
+
     bool should_have_control_avatar = false;
     if (is_animated_object)
     {

indra/newview/llvovolume.cpp

@@ -5494,6 +5494,11 @@ void LLVolumeGeometryManager::rebuildGeom(LLSpatialGroup* group)
     LL_PROFILE_ZONE_SCOPED_CATEGORY_VOLUME;
     llassert(!gCubeSnapshot);
 
+    if (group->isDead())
+    {
+        return;
+    }
+
 	if (group->changeLOD())
 	{
 		group->mLastUpdateDistance = group->mDistance;
@@ -5577,7 +5582,7 @@ void LLVolumeGeometryManager::rebuildGeom(LLSpatialGroup* group)
 	
 			LLVOVolume* vobj = drawablep->getVOVolume();
             
-			if (!vobj)
+			if (!vobj || vobj->isDead())
 			{
 				continue;
 			}