[psaux] Avoid slow PS font parsing in case of error.

Reported as

  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=9955

* src/psaux/psobjs.c (ps_parser_to_bytes): Set `parser->cursor' even
in case of error to avoid potential re-scanning.

ChangeLog

@@ -1,4 +1,15 @@
-2018-08-14  Werner Lemberg  <wl@gnu.org>
+2018-08-18  Werner Lemberg  <wl@gnu.org>
+
+	[psaux] Avoid slow PS font parsing in case of error.
+
+	Reported as
+
+	  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=9955
+
+	* src/psaux/psobjs.c (ps_parser_to_bytes): Set `parser->cursor' even
+	in case of error to avoid potential re-scanning.
+
+2018-08-18  Werner Lemberg  <wl@gnu.org>
 
 	[cff] Fix heap buffer overflow in old engine.
 

src/psaux/psobjs.c

@@ -1447,6 +1447,8 @@
                                           bytes,
                                           max_bytes );
 
+    parser->cursor = cur;
+
     if ( delimiters )
     {
       if ( cur < parser->limit && *cur != '>' )
@@ -1456,11 +1458,9 @@
         goto Exit;
       }
 
-      cur++;
+      parser->cursor++;
     }
 
-    parser->cursor = cur;
-
   Exit:
     return error;
   }