Codechange: Specify underlying type for all enums excluding those exposed to scripts. (#13383)

src/network/network_content_gui.cpp

@@ -320,7 +320,7 @@ struct ContentListFilterData {
 };
 
 /** Filter criteria for NetworkContentListWindow. */
-enum ContentListFilterCriteria {
+enum ContentListFilterCriteria : uint8_t {
 	CONTENT_FILTER_TEXT = 0,        ///< Filter by query sting
 	CONTENT_FILTER_TYPE_OR_SELECTED,///< Filter by being of displayed type or selected for download
 };