i965: Add missing null check in fs_visitor::dead_code_eliminate_local()

Signed-off-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Reviewed-by: Brian Paul <brianp@vmware.com>

src/mesa/drivers/dri/i965/brw_fs.cpp

@@ -2190,6 +2190,10 @@ fs_visitor::dead_code_eliminate_local()
 
    ht = _mesa_hash_table_create(mem_ctx, dead_code_hash_compare);
 
+   if (ht == NULL) {
+      return false;
+   }
+
    foreach_list_safe(node, &this->instructions) {
       fs_inst *inst = (fs_inst *)node;