libiberty: Always return NULL if d_add_substitution fails.

d_add_substitution can fail for various reasons, like when the subs array
is full. If d_add_substitution fails d_substitution should return NULL
early and not try to continue. Every other call of d_add_substitution
is handled in the same way.

libiberty/ChangeLog:

	* cp-demangle.c (d_substitution): Return NULL if d_add_substitution
	fails.

From-SVN: r247055

libiberty/ChangeLog

 2017-04-21  Mark Wielaard  <mark@klomp.org>
 
+	* cp-demangle.c (d_substitution): Return NULL if d_add_substitution
+	fails.
+
+2017-04-21  Mark Wielaard  <mark@klomp.org>
+
 	* cp-demangle.h (struct d_info): Remove did_subs field.
 	* cp-demangle.c (struct d_info_checkpoint): Likewise.
 	(d_template_param): Don't update did_subs.

libiberty/cp-demangle.c

@@ -3891,7 +3891,8 @@ d_substitution (struct d_info *di, int prefix)
 		  /* If there are ABI tags on the abbreviation, it becomes
 		     a substitution candidate.  */
 		  dc = d_abi_tags (di, dc);
-		  d_add_substitution (di, dc);
+		  if (! d_add_substitution (di, dc))
+		    return NULL;
 		}
 	      return dc;
 	    }