Fix issue with info and refresh
In certain cases, the `info` ioslave need to redirect to another URL
(for instance, `info:cp` is redirected to `info:/coreutils/cp invocation`). To do
so the ioslave produces an HTML page with a <meta> element having a
content-type=refresh attribute which points to the correct URL.
This causes a significant problem with the WebEnginePartHtmlEmbedder: this class
uses a QWebEnginePage to parse the HTML, but QWebEnginePage does much more than
just parsing the HTML and tries to actually refresh the page. This means that
the loadFinished signal is emitted more than once, one for the original code and
another for the refresh. Due to everything QWebEnginePage does being
asynchronous, this somehow (I couldn't exactly understand what's happening)
causes an error message saying that the page doesn't exist (I guess that
QWebEnginePage enter a loop which it forcefully breaks after a few iterations).
Disconnecting the QWebEnginePage::loadFinished signal the first time it's
emitted and connecting to it again from
WebEnginePartHtmlEmbedder::startEmbedding seems to solve the issue (at least
most of the times).