Fix null deref when generating feedback report

There was a crash report indicating this was a null deref, and the code
clearly shows the calling function can return a null pointer so account
for that case.

Bug: chromium:990507
Test: Builds
Change-Id: I3b78de23dca40637661d1a9619adf9c00593c485
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1733739
Commit-Queue: Jeffrey Kardatzke <jkardatzke@google.com>
Auto-Submit: Jeffrey Kardatzke <jkardatzke@google.com>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684073}

chrome/browser/feedback/feedback_dialog_utils.cc

@@ -34,8 +34,10 @@ GURL GetTargetTabUrl(SessionID session_id, int index) {
         browser->tab_strip_model()->GetWebContentsAt(index);
     if (target_tab) {
       if (browser->is_devtools()) {
-        target_tab = DevToolsWindow::AsDevToolsWindow(target_tab)
-                         ->GetInspectedWebContents();
+        if (auto* dev_tools_window =
+                DevToolsWindow::AsDevToolsWindow(target_tab)) {
+          target_tab = dev_tools_window->GetInspectedWebContents();
+        }
       }
       if (target_tab)
         return target_tab->GetURL();