[VarDumper] Backport handler lock when using VAR_DUMPER_FORMAT

Author: ogizanagi

DataCollector/DumpDataCollector.php

@@ -235,13 +235,7 @@ public function __destruct()
                 --$i;
             }
 
-            if (isset($_SERVER['VAR_DUMPER_FORMAT'])) {
-                $html = 'html' === $_SERVER['VAR_DUMPER_FORMAT'];
-            } else {
-                $html = !\in_array(\PHP_SAPI, ['cli', 'phpdbg'], true) && stripos($h[$i], 'html');
-            }
-
-            if ($html) {
+            if (!\in_array(\PHP_SAPI, ['cli', 'phpdbg'], true) && stripos($h[$i], 'html')) {
                 $dumper = new HtmlDumper('php://output', $this->charset);
                 $dumper->setDisplayOptions(['fileLinkFormat' => $this->fileLinkFormat]);
             } else {