Fix bug #63596: finally in generators segfaults

EX(fast_ret) wasn't initialized in this case so the code ended up
dereferencing an invalid pointer after the jump.

Zend/tests/generators/finally_ran_on_close.phpt

@@ -5,14 +5,18 @@ finally is run even if a generator is closed mid-execution
 
 function gen() {
     try {
-        echo "before yield\n";
-        yield;
-        echo "after yield\n";
+        try {
+            echo "before yield\n";
+            yield;
+            echo "after yield\n";
+        } finally {
+            echo "finally run\n";
+        }
+        echo "code after finally\n";
     } finally {
-        echo "finally run\n";
+        echo "second finally run\n";
     }
-
-    echo "code after finally\n";
+    echo "code after second finally\n";
 }
 
 $gen = gen();
@@ -23,3 +27,4 @@ unset($gen);
 --EXPECT--
 before yield
 finally run
+second finally run

Zend/zend_generators.c

@@ -60,6 +60,7 @@ void zend_generator_close(zend_generator *generator, zend_bool finished_executio
 				 * the resume. */
 				if (finally_op_num) {
 					execute_data->opline = &op_array->opcodes[finally_op_num];
+					execute_data->fast_ret = NULL;
 					generator->flags |= ZEND_GENERATOR_FORCED_CLOSE;
 					zend_generator_resume(generator TSRMLS_CC);
 					return;