SDLCursorManager: fix possibly invalid read when no cursor present

On android we have no cursor so I moved the check closer to usage

components/sdlutil/sdlcursormanager.cpp

@@ -203,19 +203,14 @@ namespace SDLUtil
     void SDLCursorManager::cursorChanged(const std::string& name)
     {
         mCurrentCursor = name;
-
-        CursorMap::const_iterator curs_iter = mCursorMap.find(name);
-
-        if(curs_iter != mCursorMap.end())
-        {
-            //we have this cursor
         _setGUICursor(name);
     }
-    }
 
     void SDLCursorManager::_setGUICursor(const std::string &name)
     {
-        SDL_SetCursor(mCursorMap.find(name)->second);
+        auto it = mCursorMap.find(name);
+        if (it != mCursorMap.end())
+            SDL_SetCursor(it->second);
     }
 
     void SDLCursorManager::createCursor(const std::string& name, int rotDegrees, osg::Image* image, Uint8 hotspot_x, Uint8 hotspot_y)