Fix #35139] Output panel options are not taken into account when you safe your render (JPG)

Was caused by svn rev53181, and it worked before because
image buffer didn't have quality set and in this case
fall back to scene settings happened.

Now or render result quality from scene settings is always
used, image buffer's settings is ignored.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56376 954f8c5b-7b00-dc11-b283-0030488c597c