Fix crash when an included .xaml file is on a different drive than the project being processed.
Fix crash when an included .xaml file is on a different drive than the project being processed.

controlflow/SourceBrowser,drose-d2l/SourceBrowser,controlflow/SourceBrowser,KirillOsenkov/SourceBrowser,drose-d2l/SourceBrowser,akrisiun/SourceBrowser,akrisiun/SourceBrowser,KirillOsenkov/SourceBrowser,akrisiun/SourceBrowser,KirillOsenkov/SourceBrowser,controlflow/SourceBrowser,drose-d2l/SourceBrowser,controlflow/SourceBrowser,akrisiun/SourceBrowser,drose-d2l/SourceBrowser,KirillOsenkov/SourceBrowser