Drop pi nodes for both old/new pred in replace_predecessor

We also need to drop pi nodes for new_pred here, as the pi node
restriction for new_pred is not necessarily true for control
coming from old_pred as well.

Fixes oss-fuzz #40782.

Author: nikic

Zend/tests/replace_pred_pi_node.phpt

@@ -7,6 +7,11 @@ function test(bool $a, bool $b) {
     if ($a && $byte > 0 && $b) {}
     unknown($byte);
 }
+function test2() {
+    foreach (0 as $v) {
+        $v ??= 0;
+    }
+}
 ?>
 ===DONE===
 --EXPECT--

ext/opcache/Optimizer/dfa_pass.c

@@ -596,7 +596,7 @@ static void replace_predecessor(zend_ssa *ssa, int block_id, int old_pred, int n
 		/* Also remove the corresponding phi node entries */
 		for (phi = ssa->blocks[block_id].phis; phi; phi = phi->next) {
 			if (phi->pi >= 0) {
-				if (phi->pi == old_pred) {
+				if (phi->pi == old_pred || phi->pi == new_pred) {
 					zend_ssa_rename_var_uses(
 						ssa, phi->ssa_var, phi->sources[0], /* update_types */ 0);
 					zend_ssa_remove_phi(ssa, phi);