Fix crash in LLControlAvatar::matchVolumeTransform() from Kitty Barnett

indra/newview/llcontrolavatar.cpp

@@ -325,6 +325,20 @@ void LLControlAvatar::markForDeath()
     mRootVolp = NULL;
 }
 
+void LLControlAvatar::markDead()
+{
+	// NOTE: this can happen when the control avatar and root volume are on different regions and we're
+		//       being called from the LLViewerRegion destructor due the region being dropped
+		//       (due to being used as a vehicle and the move not yet being processed?)
+	if (mRootVolp)
+	{
+		mRootVolp->unlinkControlAvatar();
+		mRootVolp = nullptr;
+	}
+
+	LLVOAvatar::markDead();
+}
+
 void LLControlAvatar::idleUpdate(LLAgent &agent, LLWorld &world, const F64 &time)
 {
     if (mMarkedForDeath)

indra/newview/llcontrolavatar.h

@@ -52,6 +52,7 @@ public:
     // Delayed kill so we don't make graphics pipeline unhappy calling
     // markDead() inside other graphics pipeline operations.
     void markForDeath();
+    void markDead() override;
 
     void idleUpdate(LLAgent &agent, LLWorld &world, const F64 &time) override;
 	BOOL updateCharacter(LLAgent &agent) override;