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>

models/attachment.go

@@ -99,7 +99,7 @@ func (a *Attachment) LinkedRepository() (*Repository, UnitType, error) {
 func NewAttachment(attach *Attachment, buf []byte, file io.Reader) (_ *Attachment, err error) {
 	attach.UUID = gouuid.New().String()
 
-	size, err := storage.Attachments.Save(attach.RelativePath(), io.MultiReader(bytes.NewReader(buf), file))
+	size, err := storage.Attachments.Save(attach.RelativePath(), io.MultiReader(bytes.NewReader(buf), file), -1)
 	if err != nil {
 		return nil, fmt.Errorf("Create: %v", err)
 	}