Fix class name in warning of frameless calls (#13619)

Zend/tests/frameless_bug_001.phpt

@@ -0,0 +1,19 @@
+--TEST--
+Frameless bug 001
+--FILE--
+<?php
+
+namespace NS;
+
+class Test {
+    public function test() {
+        return preg_match('foo', 'bar');
+    }
+}
+
+$test = new Test();
+$test->test();
+
+?>
+--EXPECTF--
+Warning: preg_match(): Delimiter must not be alphanumeric, backslash, or NUL byte in %s on line %d

Zend/zend_execute_API.c

@@ -507,7 +507,7 @@ ZEND_API const char *get_active_class_name(const char **space) /* {{{ */
 		return "";
 	}
 
-	func = EG(current_execute_data)->func;
+	func = zend_active_function();
 
 	switch (func->type) {
 		case ZEND_USER_FUNCTION: