Subprocess - OnBrowserCreated handle extraInfo being null

- Looks like when Chromium creates it's own windows we don't get a reference to the object

Issue #4963

Author: amaitland

CefSharp.BrowserSubprocess.Core/CefAppUnmanagedWrapper.cpp

@@ -63,6 +63,11 @@ namespace CefSharp
             //Multiple CefBrowserWrappers created when opening popups
             _browserWrappers->TryAdd(browser->GetIdentifier(), wrapper);
 
+            if (!extraInfo.get())
+            {
+                return;
+            }
+
             //For the main browser only we check LegacyBindingEnabled and
             //load the objects. Popups don't send this information and checking
             //will override the _legacyBindingEnabled field