Update booting.aspx

Throw the exception immediately if the parameter is not there or empty.

If the parameter is not there it's defaulted to the current url, and this will redirect to itself and create an endless loop here.
Merge pull request #284 from markvantilburg/patch-1

Update booting.aspx
Merge remote-tracking branch 'origin/7.0.2' into 7.1.0