polymorph into a non-twoweapon form

- you can't twoweapon unless your form allows it, but polymorph wouldn't
disable twoweapon mode immediately

doc/fixes34.1

@@ -33,6 +33,8 @@ if an unknown rolling boulder trap kills a monster, you shouldn't be a murderer
 touchstone entry in data.base
 specific message for engraving headstone with wand of digging
 wielded/quivered chained ball should be unwielded when thrown
+polymorphing into a form that cannot twoweapon should immediately disable
+	twoweapon mode
 
 
 Platform- and/or Interface-Specific Fixes

src/polyself.c

@@ -668,6 +668,8 @@ int alone;
 		    dropx(otmp2);
 	    }
 	    untwoweapon();
+	} else if (!could_twoweap(youmonst.data)) {
+	    untwoweapon();
 	}
     }
 }