composer: Center "drop files here" message
The "Drop files here to add them as attachments" message was not centered as it should have been, because the "expand" child property was reset to false when it was removed/readded to its parent.
The "Drop files here to add them as attachments" message was not centered as it should have been, because the "expand" child property was reset to false when it was removed/readded to its parent.