TileImage: refactor: s/readTileImage/readTileImageM

this method is called in the context of the parent tag;
it reads all <image> tags that are children of the current tag
and only returns one of them

src/micropolisj/gui/TileImages.java

@@ -100,7 +100,7 @@ public class TileImages
 			}
 
 			String tileName = in.getAttributeValue(null, "name");
-			TileImage img = readTileImage(in, ctx);
+			TileImage img = readTileImageM(in, ctx);
 
 			assert tileName != null;
 			assert img != null;