modules: Skip empty lines in modules.txt

Closes #13084

modules/collect.go

@@ -556,6 +556,9 @@ func (c *collector) collectModulesTXT(owner Module) error {
 		line := scanner.Text()
 		line = strings.Trim(line, "# ")
 		line = strings.TrimSpace(line)
+		if line == "" {
+			continue
+		}
 		parts := strings.Fields(line)
 		if len(parts) != 2 {
 			return fmt.Errorf("invalid modules list: %q", filename)