Add size to Save function (#15264) (#15271)

Backport #15264

This PR proposes an alternative solution to #15255 - just add the size to the
save function. Yes it is less apparently clean but it may be more correct.

Close #15255
Fix #15253

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/storage/local.go

@@ -65,7 +65,7 @@ func (l *LocalStorage) Open(path string) (Object, error) {
 }
 
 // Save a file
-func (l *LocalStorage) Save(path string, r io.Reader) (int64, error) {
+func (l *LocalStorage) Save(path string, r io.Reader, size int64) (int64, error) {
 	p := filepath.Join(l.dir, path)
 	if err := os.MkdirAll(filepath.Dir(p), os.ModePerm); err != nil {
 		return 0, err