offscreen: Plug a leak in an error path
offscreen: Plug a leak in an error path

When creating a CoglOffscreen we take a reference on the texture handle,
but in case of error we never release it.

We should take that reference only on success.

http://bugzilla.clutter-project.org/show_bug.cgi?id=2620

gcampax/cogl,collects/cogl,Distrotech/cogl,djdeath/cogl,spatulasnout/cogl,Distrotech/cogl,Distrotech/cogl,gcampax/cogl,spatulasnout/cogl,gcampax/cogl,collects/cogl,djdeath/cogl-android,djdeath/cogl-android,gcampax/cogl,Distrotech/cogl,djdeath/cogl-android,djdeath/cogl,djdeath/cogl