fix issue #1436 - object_from_map() vs Hallu

Issue reported by janne-hmp:  examining an object on the map while
halluicinating might operate on an object whose name is Null since the
random object could be one that holds an extra description for item
shuffling at game start.  Attempting to format the object led to a
crash.

I wasn't able to reproduce the crash, possibly because MacOS produces
the string "(null)" for sprintf("%s",NULL) instead of dereferencing
the Null pointer.

Perhaps random object selection for display should reject the extra
description objects in some classes.  This susbstitutes a different
object if examining the map encounters one of those.

Fixes #1436

doc/fixes3-7-0.txt

@@ -1525,6 +1525,9 @@ a vampire lord could choose to take on wolf form while flying over water or
 	lava, then revert to vampire lord form and teleport unnecessarily
 a gas spore that was killed when an engulfer swallowed it produced an explosion
 	on the map rather than inside the engulfer
+hallucination can display objects on the map that have a description (for
+	shuffling into play at game start) but no name; examining those might
+	trigger a crash
 
 
 Fixes to 3.7.0-x General Problems Exposed Via git Repository