strange object vs generic objects

Try to fix a fuzzer issue.  I wasn't able to reproduce it so am not
sure whether this actually fixes it.  A mimic seemed to be mimicking
object #1 (generic ILLOBJ_CLASS object which shouldn't occur) rather
than #0 (strange object).  Strange object always has dknown==1 and
generic objects should always have dknown==0 but farlook of mystery
object #1 had its dknown flag set.

An earlier fix to force non-Null oc_name when formatting objects in
order to pacify the static analyzer might have been the reason that
the problem couldn't be reproduced.

This includes a few miscellaneous changes made while unsuccessfully
hunting for the problem.

src/mkobj.c

@@ -789,7 +789,7 @@ unknow_object(struct obj *obj)
     obj->known = objects[obj->otyp].oc_uses_known ? 0 : 1;
 }
 
-/* mksobj(): create a specific type of object; result it always non-Null */
+/* mksobj(): create a specific type of object; result is always non-Null */
 struct obj *
 mksobj(int otyp, boolean init, boolean artif)
 {