tone_mapping: Fix inferred default tone map param
When the param is not set or zero, the default should be used before clamping, otherwise the param is left to the clamped minimum and the default param is never set.
Fixes: https://github.com/mpv-player/mpv/issues/11076
I'm not sure how to handle intentional param overrides to 0, the current code would default to the min instead.
I think defaulting to sane values makes sense.
Edited by quietvoid