known bear trap forgotton by player polymorphed into a flyer

The original report stated:

     "I located a bear trap as a human and just ignored it
     for the time. I polymporphed into a Vampire Lord, then
     went to #untrap the bear trap.  On the first attempt,
     I stood beside the trap and attempted to #untrap.  I
     received the 'Whoops!' message and automatically moved
     onto the trap square as a result. The bear trap vanished!
     I obviously wasn't trapped since I'm polymorphed into a
     flying monster, but the trap glyph was no longer present.
     The glyph looked like regular floor - as if I had
     untrapped the bear trap and taken the trap with me."

The trap was actually still there but became hidden intentionally
for other valid scenarios, but was an unintended side-effect for
this scenario.

Fix it by failing the #untrap operation for a Flyer earlier on,
and in a more benign manner, since the Flyer ultimately doesn't
end up in the trap anyway.  You'll still get the "Whoops!",
followed by a message, but that's as far as the "failed" #untrap
attempt will go under the circumstances.

doc/fixes36.2

@@ -136,6 +136,9 @@ gremlins seemed impervious to Sunsword's light yet a flash from a camera
 when objects migrate (fall down stairs) and invisible hero (w/o see invisible,
 	no-autopickup) descends, stairs get shown instead of object(s) on them
 drum of earthquake was causing deafness but oddly enough only when used up
+known bear trap was being forgotten about by a player polymorphed into a
+	flying monster if the player unsuccessfully tried to #untrap it and
+	moved onto the trap square as a result
 
 
 Fixes to Post-3.6.1 Problems that Were Exposed Via git Repository

src/trap.c

@@ -3991,6 +3991,16 @@ boolean force_failure;
                 }
             } else if (under_u) {
                 dotrap(ttmp, 0);
+            } else if (ttype == BEAR_TRAP && (Levitation || Flying)) {
+                /* There was a report of oddities of the trap
+                   vanishing from view due to tseen being cleared
+                   (which was deliberate to work around a check_here()
+                   issue). Since you won't actually end up in the trap
+                   during the #untrap operation anyway due to
+                   Levitation and Flying checks further along,
+                   just avoid the whole "vanishing trap" scenario
+                   by failing the #untrap operation right here. */
+                You("couldn't reach it from your vantage point.");
             } else {
                 move_into_trap(ttmp);
             }