[repacker] validate link widths during repacker setup.

src/graph/graph.hh

@@ -58,6 +58,13 @@ struct graph_t
         unsigned start = l.position;
         unsigned end = start + l.width - 1;
 
+        if (unlikely (l.width < 2 || l.width > 4))
+        {
+          DEBUG_MSG (SUBSET_REPACK, nullptr,
+                     "Invalid graph. Invalid link width.");
+          return false;
+        }
+
         if (unlikely (end >= table_size ()))
         {
           DEBUG_MSG (SUBSET_REPACK, nullptr,

test/fuzzing/hb-repacker-fuzzer.cc

@@ -111,8 +111,6 @@ extern "C" int LLVMFuzzerTestOneInput (const uint8_t *data, size_t size)
     if (links[i].parent >= num_objects
         || links[i].child > links[i].parent) // Enforces DAG graph
       goto end;
-
-    if (links[i].width < 2 || links[i].width > 4) goto end;
   }
 
   add_links_to_objects (objects, num_objects,