Fix invalid regexp serialization

Invalid regexps were serialized as empty regexps, which match any expression, while invalid regexp should not match anything.

internal/base/SerializableHelpers.go

@@ -19,7 +19,11 @@ func NewRegexp(pattern string) Regexp {
 }
 func (x Regexp) Valid() bool { return x.Regexp != nil }
 func (x *Regexp) Set(in string) (err error) {
-	x.Regexp, err = regexp.Compile(in)
+	if len(in) > 0 {
+		x.Regexp, err = regexp.Compile(in)
+	} else {
+		x.Regexp = nil
+	}
 	return
 }
 func (x Regexp) String() string {

utils/UFS.go

@@ -1105,8 +1105,13 @@ func MakeGlobRegexpExpr(glob ...string) string {
 	if len(glob) == 0 {
 		return ".*"
 	}
+
 	var expr strings.Builder
-	expr.WriteString("(?i)(?:") // insensitive, non-capturing group
+	expr.WriteString("(?i)") // insensitive
+	if len(glob) > 1 {       // non-capturing group
+		expr.WriteString("(?:")
+	}
+
 	for i, it := range glob {
 		it = regexp.QuoteMeta(it)
 		it = strings.ReplaceAll(it, "\\?", ".")
@@ -1121,7 +1126,10 @@ func MakeGlobRegexpExpr(glob ...string) string {
 		expr.WriteString(it)
 		expr.WriteRune(')')
 	}
-	expr.WriteString(")")
+
+	if len(glob) > 1 { // non-capturing group
+		expr.WriteRune(')')
+	}
 	return expr.String()
 }
 func MakeGlobRegexp(glob ...string) base.Regexp {