Fix NPE's

Signed-off-by: yoyosource <yoyosource@nidido.de>

BauSystem_Main/src/de/steamwar/bausystem/region/Region.java

@@ -146,6 +146,9 @@ public class Region {
         }
         if (prototype != null) {
             skin = regionData.getPlainValueOrDefault("skin", prototype.getDefaultSkin());
+            if (!prototype.getSkinMap().containsKey(skin)) {
+                skin = prototype.getDefaultSkin();
+            }
         }
         regionData.add("skin", skin);