buffer: Don't process the default syntax in the user's custom file lookup

It needs to be processed earliest in the moment no match could be determined.

internal/buffer/buffer.go

@@ -710,6 +710,10 @@ func (b *Buffer) UpdateRules() {
 	var header *highlight.Header
 	// search for the syntax file in the user's custom syntax files
 	for _, f := range config.ListRealRuntimeFiles(config.RTSyntax) {
+		if f.Name() == "default" {
+			continue
+		}
+
 		data, err := f.Data()
 		if err != nil {
 			screen.TermMessage("Error loading syntax file " + f.Name() + ": " + err.Error())