fix truncate err handling

wal.go

@@ -728,7 +728,7 @@ func (l *Log) truncateFront(index uint64) (err error) {
 	ebuf := s.ebuf[epos[0].pos:]
 	// Create a temp file contains the truncated segment.
 	tempName := filepath.Join(l.path, "TEMP")
-	err = func() error {
+	if err = func() error {
 		f, err := os.OpenFile(tempName, os.O_CREATE|os.O_RDWR|os.O_TRUNC, l.opts.FilePerms)
 		if err != nil {
 			return err
@@ -741,7 +741,9 @@ func (l *Log) truncateFront(index uint64) (err error) {
 			return err
 		}
 		return f.Close()
-	}()
+	}(); err != nil {
+		return fmt.Errorf("failed to create temp file for new start segment: %w", err)
+	}
 	// Rename the TEMP file to it's START file name.
 	startName := filepath.Join(l.path, segmentName(index)+".START")
 	if err = os.Rename(tempName, startName); err != nil {
@@ -834,7 +836,7 @@ func (l *Log) truncateBack(index uint64) (err error) {
 	ebuf := s.ebuf[:epos[len(epos)-1].end]
 	// Create a temp file contains the truncated segment.
 	tempName := filepath.Join(l.path, "TEMP")
-	err = func() error {
+	if err = func() error {
 		f, err := os.OpenFile(tempName, os.O_CREATE|os.O_RDWR|os.O_TRUNC, l.opts.FilePerms)
 		if err != nil {
 			return err
@@ -847,7 +849,9 @@ func (l *Log) truncateBack(index uint64) (err error) {
 			return err
 		}
 		return f.Close()
-	}()
+	}(); err != nil {
+		return fmt.Errorf("failed to create temp file for new end segment: %w", err)
+	}
 	// Rename the TEMP file to it's END file name.
 	endName := filepath.Join(l.path, segmentName(s.index)+".END")
 	if err = os.Rename(tempName, endName); err != nil {