time: fix timezone lookup logic for non-DST zones

Fixes golang#58682

Author: KimMachineGun

src/time/zoneinfo.go

@@ -203,7 +203,7 @@ func (l *Location) lookup(sec int64) (name string, offset int, start, end int64,
 	// If we're at the end of the known zone transitions,
 	// try the extend string.
 	if lo == len(tx)-1 && l.extend != "" {
-		if ename, eoffset, estart, eend, eisDST, ok := tzset(l.extend, end, sec); ok {
+		if ename, eoffset, estart, eend, eisDST, ok := tzset(l.extend, start, sec); ok {
 			return ename, eoffset, estart, eend, eisDST
 		}
 	}

src/time/zoneinfo_read.go

@@ -329,7 +329,7 @@ func LoadLocationFromTZData(name string, data []byte) (*Location, error) {
 			} else if l.extend != "" {
 				// If we're at the end of the known zone transitions,
 				// try the extend string.
-				if name, offset, estart, eend, isDST, ok := tzset(l.extend, l.cacheEnd, sec); ok {
+				if name, offset, estart, eend, isDST, ok := tzset(l.extend, l.cacheStart, sec); ok {
 					l.cacheStart = estart
 					l.cacheEnd = eend
 					// Find the zone that is returned by tzset to avoid allocation if possible.