fix: slice out of range by @robfig/cronrobfig/pull/482

Author: fufuok

parser.go

@@ -94,6 +94,10 @@ func (p Parser) Parse(spec string) (Schedule, error) {
 	if strings.HasPrefix(spec, "TZ=") || strings.HasPrefix(spec, "CRON_TZ=") {
 		var err error
 		i := strings.Index(spec, " ")
+		if i < 0 {
+			return nil, fmt.Errorf("invalid spec string")
+		}
+
 		eq := strings.Index(spec, "=")
 		if loc, err = time.LoadLocation(spec[eq+1 : i]); err != nil {
 			return nil, fmt.Errorf("provided bad location %s: %v", spec[eq+1:i], err)