MBF21: The `comp_ledgeblock` blocking items moved by scroll special.

[rfomin]

This is also DSDA-Doom and MBF21 spec issue.

Bug report: [doomworld], test WAD: scrolltest.zip. A potential fix is to move the reset of the MIF_SCROLLING flag somewhere else, perhaps when if (!(mobj->momx | mobj->momy))? https://github.com/fabiangreffrath/woof/blob/1d7cb3072fbd0d0d05eb293f3242b26165b2c302/src/p_mobj.c#L734