Engine: fixed a condition in movelist_handle_remainer()

Should compare xpermove and ypermove using abs values, as they may have different signs.

Engine/main/update.cpp

@@ -104,9 +104,10 @@ static void movelist_handle_remainer(const fixed xpermove, const fixed ypermove,
     const int xdistance, const float step_length, fixed &fin_ymove, float &fin_from_part)
 {
     // Walk along the remaining axis with the full walking speed
-    assert(xpermove != 0 && ypermove != 0);
+    assert(xpermove != 0 && ypermove != 0 && step_length >= 0.f);
     fin_ymove = ypermove > 0 ? ftofix(step_length) : -ftofix(step_length);
     fin_from_part = (float)xdistance / fixtof(xpermove);
+    assert(fin_from_part >= 0);
 }
 
 // Handle remaining move fixup, but only if necessary
@@ -119,11 +120,11 @@ static void movelist_handle_remainer(MoveList &m)
     // Apply remainer to movelists where LONGER axis was completed, and SHORTER remains
     if ((xpermove != 0) && (ypermove != 0))
     {
-        if ((m.doneflag & kMoveListDone_XY) == kMoveListDone_X && (ypermove < xpermove))
-            movelist_handle_remainer(xpermove, ypermove, target.X - m.from.X,
+        if ((m.doneflag & kMoveListDone_XY) == kMoveListDone_X && (abs(ypermove) < abs(xpermove)))
+            movelist_handle_remainer(xpermove, ypermove, (target.X - m.from.X),
                 m.GetStepLength(), m.fin_move, m.fin_from_part);
-        else if ((m.doneflag & kMoveListDone_XY) == kMoveListDone_Y && (xpermove < ypermove))
-            movelist_handle_remainer(ypermove, xpermove, target.Y - m.from.Y,
+        else if ((m.doneflag & kMoveListDone_XY) == kMoveListDone_Y && (abs(xpermove) < abs(ypermove)))
+            movelist_handle_remainer(ypermove, xpermove, (target.Y - m.from.Y),
                 m.GetStepLength(), m.fin_move, m.fin_from_part);
     }
 }