fix #H2154 - unlocking door blocked by mimic-as-boulder (trunk only)

Reported five months ago by <email deleted>,
the top level of Sokoban has mimics who pose as boulders and if one was
in a doorway (treasure zoo at final destination) you could still unlock
the door there without waking the mimic.  Yesterday's fix for unlocking
a door which was actually a mimic posing as one didn't handle this case.

doc/fixes35.0

@@ -342,6 +342,8 @@ when reading an unknown scroll and learning it, discovery of teleporation was
 	too late if hero happened to land on another scroll of teleportation
 using an unlocking tool on a closed door which was actually a mimic reported
 	that there was no door to unlock instead of exposing the mimic
+using an unlocking tool on a boulder that was a mimic in a Sokoban doorway
+	successfully unlocked the underlying door without exposing mimic
 
 
 Platform- and/or Interface-Specific Fixes

src/lock.c

@@ -407,6 +407,17 @@ pick_lock(pick)
 		/* "The door actually was a <mimic>!" */
 		stumble_onto_mimic(mtmp);
 		return PICKLOCK_LEARNED_SOMETHING;
+	    /* mimic-as-boulder on last Sokoban level */
+	    } else if (mtmp && mtmp->m_ap_type == M_AP_OBJECT &&
+			mtmp->mappearance == BOULDER) {
+		if (Blind)	/* by touch */
+		    /* "Wait!  That's a monster!" */
+		    stumble_onto_mimic(mtmp);
+		else if (IS_DOOR(door->typ))
+		    pline("That door is blocked.");
+		else
+		    You("see no door there.");
+		return PICKLOCK_LEARNED_SOMETHING;
 	    }
 	    if(!IS_DOOR(door->typ)) {
 		if (is_drawbridge_wall(cc.x,cc.y) >= 0)