IEUrlExtension: Add tests for the main use case the lib exists for

IEUrlExtension: Add tests for the main use case the lib exists for

There are plenty of tests for the basic behaviour of the extension
detector and how IE favours the extension from the first question mark
segment that has a dot in the next segment.

But it was missing a test for the main use case the library exists
for, which is extensions in query strings when there is a file name
with extension already (but the dot is urlencoded).

Change-Id: I0f2e1387ae42da68020f1d793bb9eb5a87a06f24