Fix nil pointer panic in commonLock defer

The defer function in commonLock calls file.Close() when an error
occurs, but file is always nil at that point. If os.Open or
os.OpenFile fails, file is nil. If platformSpecificLock fails, file
is closed inline and then set to nil by the return statement. In
both cases, calling file.Close() in the defer panics on a nil
pointer. Add nil check before file.Close() in the defer.

Signed-off-by: Federico Bramucci <163430291+fedebram@users.noreply.github.com>

Author: fedebram

pkg/internal/filesystem/lock.go

@@ -51,7 +51,11 @@ func ReadOnlyLock(path string) (file *os.File, err error) {
 func commonlock(path string, mode lockType) (file *os.File, err error) {
 	defer func() {
 		if err != nil {
-			err = errors.Join(ErrLockFail, err, file.Close())
+			if file != nil {
+				err = errors.Join(ErrLockFail, err, file.Close())
+			} else {
+				err = errors.Join(ErrLockFail, err)
+			}
 		}
 	}()