Avoid op_num = -1 in unfinished generator cleanup

Also add two tests showing that the -1 substraction in the
computation of op_num is really necessary.

Author: nikic

Zend/tests/generators/aborted_yield_during_nested_fcalls.phpt

@@ -0,0 +1,18 @@
+--TEST--
+Aborted yield during nested calls
+--FILE--
+<?php
+
+function func() {}
+
+function gen($x) {
+    func(func($x, $x, func($x, yield)));
+}
+
+$gen = gen("x");
+$gen->rewind();
+
+?>
+===DONE===
+--EXPECT--
+===DONE===

Zend/tests/generators/aborted_yield_during_switch.phpt

@@ -0,0 +1,19 @@
+--TEST--
+Aborted yield during switch
+--FILE--
+<?php
+
+function gen($x) {
+    switch ($x."y") {
+        default:
+            yield;
+    }
+}
+
+$gen = gen("x");
+$gen->rewind();
+
+?>
+===DONE===
+--EXPECT--
+===DONE===

Zend/zend_generators.c

@@ -34,15 +34,16 @@ static zend_object *zend_generator_create(zend_class_entry *class_type);
 static void zend_generator_cleanup_unfinished_execution(zend_generator *generator) /* {{{ */
 {
 	zend_execute_data *execute_data = generator->execute_data;
-	/* -1 required because we want the last run opcode, not the next to-be-run one. */
-	uint32_t op_num = execute_data->opline - execute_data->func->op_array.opcodes - 1;
 
 	if (generator->send_target) {
-		if (Z_REFCOUNTED_P(generator->send_target)) Z_DELREF_P(generator->send_target);
+		Z_TRY_DELREF_P(generator->send_target);
 		generator->send_target = NULL;
 	}
 
-	{
+	if (execute_data->opline != execute_data->func->op_array.opcodes) {
+		/* -1 required because we want the last run opcode, not the next to-be-run one. */
+		uint32_t op_num = execute_data->opline - execute_data->func->op_array.opcodes - 1;
+
 		/* There may be calls to zend_vm_stack_free_call_frame(), which modifies the VM stack
 		 * globals, so need to load/restore those. */
 		zend_vm_stack original_stack = EG(vm_stack);