steed fixes

A relatively recent change to prevent #ride letting you move in
a way you could walk (squeeze through a tight a gap or enter doorway
diagonally) resulted in crashing due to access violation or segfault
if you tried to mount toward a spot that didn't contain any monster.
Noticed while testing saddle cursing; tried to mount while stunned....

     Also, if the character had a saddle "worn" in weapon, alternate
weapon, or quiver slot, it didn't get unworn when applying the saddle
to a mount.  The next time the player tried to equip something in the
same slot there'd be a warning message; I don't know whether any more
serious symptoms could occur.

src/steed.c

@@ -132,6 +132,7 @@ use_saddle(otmp)
 	/* Make the attempt */
 	if (rn2(100) < chance) {
 	    You("put the saddle on %s.", mon_nam(mtmp));
+	    if (otmp->owornmask) remove_worn_item(otmp, FALSE);
 	    freeinv(otmp);
 	    /* mpickobj may free otmp it if merges, but we have already
 	       checked for a saddle above, so no merger should happen */
@@ -230,6 +231,13 @@ mount_steed(mtmp, force)
 	}
 
 	/* Can the player reach and see the monster? */
+	if (!mtmp || (!force && ((Blind && !Blind_telepat) ||
+		mtmp->mundetected ||
+		mtmp->m_ap_type == M_AP_FURNITURE ||
+		mtmp->m_ap_type == M_AP_OBJECT))) {
+	    pline("I see nobody there.");
+	    return (FALSE);
+	}
 	if (u.uswallow || u.ustuck || u.utrap || Punished ||
 	    !test_move(u.ux, u.uy, mtmp->mx-u.ux, mtmp->my-u.uy, TEST_MOVE)) {
 	    if (Punished || !(u.uswallow || u.ustuck || u.utrap))
@@ -238,13 +246,6 @@ mount_steed(mtmp, force)
 		You("are stuck here for now.");
 	    return (FALSE);
 	}
-	if (!mtmp || (!force && ((Blind && !Blind_telepat) ||
-		mtmp->mundetected ||
-		mtmp->m_ap_type == M_AP_FURNITURE ||
-		mtmp->m_ap_type == M_AP_OBJECT))) {
-	    pline("I see nobody there.");
-	    return (FALSE);
-	}
 
 	/* Is this a valid monster? */
 	otmp = which_armor(mtmp, W_SADDLE);
@@ -487,7 +488,8 @@ dismount_steed(reason)
 	    case DISMOUNT_BYCHOICE:
 	    default:
 		if (otmp && otmp->cursed) {
-		    You("can't.  The saddle seems to be cursed.");
+		    You("can't.  The saddle %s cursed.",
+			otmp->bknown ? "is" : "seems to be");
 		    otmp->bknown = TRUE;
 		    return;
 		}