Evas filters: fix black squares with the GL engine

Evas filters: fix black squares with the GL engine

If a text object changes regularily, there might be cases where
the object will be rendered as a simple black rectangle for just
one frame.

It seems that the previous output buffer is deleted before being
actually rendered on screen. This patch will delay the deletion
of the previous buffer until the current one has been rendered
to the target surface.

And again, thanks zmike for reporting.

@fix

Signed-off-by: Jean-Philippe Andre <jp.andre@samsung.com>