parser.go: added recover from panic in parser.Parse()

parser.go

@@ -382,6 +382,16 @@ func (parser *parser) parseItem(scanner *scanner, ctx parserContext, termSymbols
 }
 
 func (parser *parser) Parse(scanner *scanner, termSymbols ...Symbol) (tree *ast, err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			if errVal, ok := r.(error); ok {
+				err = errVal
+			}
+		}
+		if err == nil {
+			err = errors.New("unexpected error while parsing the expression")
+		}
+	}()
 	termSymbols = append(termSymbols, SymEos)
 	return parser.parseGeneral(scanner, allowMultiExpr, termSymbols...)
 }