[pshinter] Fix numeric overflow.

Reported as

  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=11242

* src/pshinter/pshrec.c (ps_dimension_add_t1stem): Implement it.

ChangeLog

@@ -1,3 +1,13 @@
+2018-11-06  Werner Lemberg  <wl@gnu.org>
+
+	[pshinter] Fix numeric overflow.
+
+	Reported as
+
+	  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=11242
+
+	* src/pshinter/pshrec.c (ps_dimension_add_t1stem): Implement it.
+
 2018-11-06  Werner Lemberg  <wl@gnu.org>
 
 	[psaux] Fix timeout in old CFF engine.

src/pshinter/pshrec.c

@@ -666,7 +666,7 @@
       if ( len == -21 )
       {
         flags |= PS_HINT_FLAG_BOTTOM;
-        pos   += len;
+        pos    = ADD_INT( pos, len );
       }
       len = 0;
     }