Mass: not all parts can have 8 decals in the demo.

For now, at least. Just like the code that treats a lack of global
styles as a demo thing, I'll remove it in due time.

src/Mass/Mass.cpp

@@ -585,8 +585,7 @@ void Mass::getArmourParts() {
         }
 
         if(decals_array->items.size() != 8) {
-            _state = State::Invalid;
-            return;
+            _demo = true;
         }
 
         for(UnsignedInt j = 0; j < decals_array->items.size(); j++) {