Made lensfun lookups for one lens really unique.  Fixes bug #9662.

Please review the first hunk thoroughly because I don't understand what "commit_params" does.

The second hunk is actually solving the issue: autoscaling now works also for lenses with multiple calibration entries in lensfun, e.g. the Canon 50mm f/1.4 on an APS-C camera.

And the third hunk is commented out anyway.  No idea what it does, but I'm sure that it is correct now as far as lens object lookup is concerned.