Merge branch 'p_isobjectongroundin-fixes' into 'next'

Fixes for Each Time and P_IsObjectOnGroundIn

Fixes the issue with Each Time reported here: https://mb.srb2.org/showthread.php?t=42818

Also fixes a separate issue with P_IsObjectOnGroundIn and intangible FOFs (where it determined that standing at the top height of them counted as being on the ground) which was also reproducable via the above bug funnily enough.

See merge request !204