When uploading a picture to a texture, glamor_upload_picture_to_texture
calls glamor_pixmap_ensure_fbo to ensure that there is backing FBO.
The FBO will be allocated if the picture's drawable pixmap does not have
one already, which can fail when there is no GL memory left.

glamor_upload_picture_to_texture checks that the call succeeded and will
enter the failure path if it did not. However, unlike many other
functions in glamor, this one has ret set to TRUE initially, so it needs
to be set to FALSE when a failure happens.

Otherwise, the error is not propagated and the failure path return TRUE.
This leads to a fault when trying to access the FBO pointer later on.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>