fdo#72156: GraphicObject: Added missing delete of stream

Change-Id: I1b84941b0e4b17d5819b1e4af0da9ce3f673710f
Signed-off-by: Ulrich Kitzinger <ulkitz@hotmail.de>
(cherry picked from commit cc36dfc9bf4f327c359d171d8d05f0ede049164e)
Signed-off-by: Michael Stahl <mstahl@redhat.com>