Custom step height: Fix implementation

Custom step height: Fix implementation

Recent commit 45ab62d6a3d90ab3b97aec88251a766cb5dd1899 had a coding error that
made climbing out of water difficult due to an incorrect value of the step height
when not 'touching ground'.
It also incorrectly multiplied the custom stepheight by BS, resulting in being
able to step-up 2 nodes if set to the default of 0.6, or even 0.3.
Also the implementation was wrong because it customised the step height when
not 'touching ground', this step height is for a slight rise when catching the
edge of a node during a jump, and should always remain at 0.2 * BS.