[Client] Fix potential invalid pointer when storing cell unloads

Notably, builds of the client done with Clang were crashing on startup before this.

apps/openmw/mwmp/LocalPlayer.cpp

@@ -1544,7 +1544,7 @@ void LocalPlayer::clearCurrentContainer()
     currentContainer.mpNum = 0;
 }
 
-void LocalPlayer::storeCellState(ESM::Cell cell, int stateType)
+void LocalPlayer::storeCellState(const ESM::Cell& cell, int stateType)
 {
     std::vector<CellState>::iterator iter;
 

apps/openmw/mwmp/LocalPlayer.hpp

@@ -91,7 +91,7 @@ namespace mwmp
         void clearCellStates();
         void clearCurrentContainer();
 
-        void storeCellState(ESM::Cell cell, int stateType);
+        void storeCellState(const ESM::Cell& cell, int stateType);
         void storeCurrentContainer(const MWWorld::Ptr& container);
 
         void playAnimation();

apps/openmw/mwworld/scene.cpp

@@ -243,6 +243,17 @@ namespace MWWorld
         std::cout << "Unloading cell\n";
         ListAndResetObjectsVisitor visitor;
 
+        /*
+            Start of tes3mp addition
+
+            Set a const pointer to the iterator's ESM::Cell here, because
+            (*iter)->getCell() can become invalid later down
+        */
+        const ESM::Cell* cell = (*iter)->getCell();
+        /*
+            End of tes3mp addition
+        */
+
         (*iter)->forEach<ListAndResetObjectsVisitor>(visitor);
         for (std::vector<MWWorld::Ptr>::const_iterator iter2 (visitor.mObjects.begin());
             iter2!=visitor.mObjects.end(); ++iter2)
@@ -276,7 +287,7 @@ namespace MWWorld
 
             Store a cell unload for the LocalPlayer
         */
-        mwmp::Main::get().getLocalPlayer()->storeCellState(*(*iter)->getCell(), mwmp::CellState::UNLOAD);
+        mwmp::Main::get().getLocalPlayer()->storeCellState(*cell, mwmp::CellState::UNLOAD);
         /*
             End of tes3mp addition
         */