in the debug mode terrain descriptions, also give the editor image

This is helpful if you are trying to figure out what to put in the
<img> tags when inserting an image for a terrain in a help entry.

src/help.cpp

@@ -1362,6 +1362,12 @@ public:
 			ss << "Light Bonus: "   << type_.light_bonus(0) << "\n";
 
 			ss << type_.income_description();
+
+			if (type_.editor_image().empty()) { // Note: this is purely temporary to help make a different help entry
+				ss << "\nEditor Image: Empty\n";
+			} else {
+				ss << "\nEditor Image: " << type_.editor_image() << "\n";
+			}
 		}
 
 		return ss.str();