Do not copy global map texture during savegame loading (bug #5308)

CHANGELOG.md

@@ -204,6 +204,7 @@
     Bug #5269: Editor: Cell lighting in resaved cleaned content files is corrupted
     Bug #5278: Console command Show doesn't fall back to global variable after local var not found
     Bug #5300: NPCs don't switch from torch to shield when starting combat
+    Bug #5308: World map copying makes save loading much slower
     Feature #1774: Handle AvoidNode
     Feature #2229: Improve pathfinding AI
     Feature #3025: Analogue gamepad movement controls

apps/openmw/mwrender/globalmap.cpp

@@ -457,7 +457,7 @@ namespace MWRender
         if (map.mImageData.empty())
             return;
 
-        Files::IMemStream istream(&map.mImageData[0], map.mImageData.size());
+        Files::IMemStream istream(map.mImageData.data(), map.mImageData.size());
 
         osgDB::ReaderWriter* readerwriter = osgDB::Registry::instance()->getReaderWriterForExtension("png");
         if (!readerwriter)
@@ -522,7 +522,7 @@ namespace MWRender
 
         if (srcBox == destBox && imageWidth == mWidth && imageHeight == mHeight)
         {
-            mOverlayImage->copySubImage(0, 0, 0, image);
+            mOverlayImage = image;
 
             requestOverlayTextureUpdate(0, 0, mWidth, mHeight, texture, true, false);
         }