Update to the latest version of the tesselator from GLU

Mesa's libGLU tesselator code has had a commit on it since it was
copied into Cogl. It sounds like it fixes a potential crash so we
should probably have it in Cogl too.

http://cgit.freedesktop.org/mesa/glu/commit/?id=bfdf99d6ff64b9c2

Reviewed-by: Robert Bragg <robert@linux.intel.com>

(cherry picked from commit c6b2429546d3ea0aa91caa47c7c90f932984ea33)

cogl/tesselator/priorityq.c

@@ -65,6 +65,7 @@ PriorityQ *pqNewPriorityQ( int (*leq)(PQkey key1, PQkey key2) )
      return NULL;
   }
 
+  pq->order = NULL;
   pq->size = 0;
   pq->max = INIT_SIZE;
   pq->initialized = FALSE;