Slightly modified fix for #622 based on https://github.com/cefsharp/CefSharp/pull/626
Update ResourceHandler.cs

Added override for passing in the file ext to correctly set the correct mime type
Merge pull request #630 from amaitland/master

Slightly modified fix for #622 based on PR #626
Added null checks for managedCefBrowserAdapter.
Merge pull request #635 from dhasi/wpf_cwb_nullRef

Added null checks for managedCefBrowserAdapter.
Merge pull request #629 from Jayman1305/patch-2

Update ResourceHandler.cs
ResourceHandler formatting change (indentation)