8268369: SIGSEGV in PhaseCFG::implicit_null_check due to missing null check

Reviewed-by: chagedorn, kvn

src/hotspot/share/opto/lcm.cpp

@@ -413,7 +413,7 @@ void PhaseCFG::implicit_null_check(Block* block, Node *proj, Node *val, int allo
   // Move the control dependence if it is pinned to not-null block.
   // Don't change it in other cases: NULL or dominating control.
   Node* ctrl = best->in(0);
-  if (get_block_for_node(ctrl) == not_null_block) {
+  if (ctrl != NULL && get_block_for_node(ctrl) == not_null_block) {
     // Set it to control edge of null check.
     best->set_req(0, proj->in(0)->in(0));
   }