safe_oname (trunk only)

There were routines that were passed the
object name as an argument.  Before the oextra
patch, ONAME() always returned a valid pointer
to a location within the obj struct. The oextra
patch worked around those cases by
using a temporary variable that was either set
to ONAME (if the obj passed the has_oname() test),
or to ""  (pointer to an empty string) if no name was
present.

Since that might be a common thing to do, provide
the safe_oname() routine that you can use as a
function parameter without having to worry about
about whether ONAME(obj) is valid, and without
the need for the temporary variable.

src/objnam.c

@@ -2942,10 +2942,7 @@ typfnd:
 	    && !wizard
 #endif
 	    ) {
-	    char *tnam = "";
-	    if (has_oname(otmp))
-	    	tnam = ONAME(otmp);
-	    artifact_exists(otmp, tnam, FALSE);
+	    artifact_exists(otmp, safe_oname(otmp), FALSE);
 	    obfree(otmp, (struct obj *) 0);
 	    otmp = &zeroobj;
 	    pline("For a moment, you feel %s in your %s, but it disappears!",