[VarDumper] Fix dumping Twig source in stack traces

Author: nicolas-grekas

DataCollector/DumpDataCollector.php

@@ -103,7 +103,7 @@ public function dump(Data $data)
                         $info = $template->getDebugInfo();
                         if (isset($info[$trace[$i - 1]['line']])) {
                             $line = $info[$trace[$i - 1]['line']];
-                            $file = method_exists($template, 'getSourceContext') ? $template->getSourceContext()->getPath() : false;
+                            $file = method_exists($template, 'getSourceContext') ? $template->getSourceContext()->getPath() : null;
 
                             if ($src) {
                                 $src = explode("\n", $src);
@@ -266,7 +266,7 @@ private function doDump($data, $name, $file, $line)
         if (PHP_VERSION_ID >= 50400 && $this->dumper instanceof CliDumper) {
             $contextDumper = function ($name, $file, $line, $fileLinkFormat) {
                 if ($this instanceof HtmlDumper) {
-                    if ('' !== $file) {
+                    if ($file) {
                         $s = $this->style('meta', '%s');
                         $name = strip_tags($this->style('', $name));
                         $file = strip_tags($this->style('', $file));