cogl-atlas-texture: Don't disable atlas if can't read texture data
cogl-atlas-texture: Don't disable atlas if can't read texture data

Previously atlasing would be disabled if the GL driver does not
support reading back texture data. This meant that atlasing would not
happen on GLES. However we also require that the driver support FBOs
and the texture data is only read back as a fallback if the FBO
fails. Therefore the atlas should be ok on GLES 2 which has FBO
support in core.

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