A spike bug no more

Jumping at spikes on FOFs in reverse gravity - most notably in ERZ3 - no longer teleports you downwards into the death pit beneath it.

src/p_map.c

@@ -994,7 +994,7 @@ static boolean PIT_CheckThing(mobj_t *thing)
if (tmthing->player && tmthing->z + tmthing->height > topz
&& tmthing->z + tmthing->height < tmthing->ceilingz)
{
-				tmfloorz = tmceilingz = INT32_MIN; // block while in air
+				tmfloorz = tmceilingz = topz; // block while in air
#ifdef ESLOPE
tmceilingslope = NULL;
#endif
@@ -1037,7 +1037,7 @@ static boolean PIT_CheckThing(mobj_t *thing)
if (tmthing->player && tmthing->z < topz
&& tmthing->z > tmthing->floorz)
{
-				tmfloorz = tmceilingz = INT32_MAX; // block while in air
+				tmfloorz = tmceilingz = topz; // block while in air
#ifdef ESLOPE
tmfloorslope = NULL;
#endif