Network process crash when running http/tests/appcache/fallback.html
https://bugs.webkit.org/show_bug.cgi?id=138740

Reviewed by Alexey Proskuryakov.

It happens because ResourceHandle::continueWillSendRequest() is
called with a null request. We could handle that case in the
ResourceHandle, but the thing is tha the behaviour is
not the same for async loads, or when loading in the web
process. In WebResourceLoader::willSendRequest(),
ResourceRequest::willSendRequest() is called, and cancels the load
if the client returns a null request. In this case, the
ResourceLoader is detached and WebResourceLoader::willSendRequest()
returns early without sending the ContinueWillSendRequest message
to the network process. However, for synchronous loads,
NetworkResourceLoader::continueWillSendRequest() is always called.

Fixes http/tests/appcache/fallback.html for GTK port when using
the network process.

* NetworkProcess/NetworkResourceLoader.cpp:
(WebKit::NetworkResourceLoader::continueWillSendRequest): Do not
call ResourceHandle::continueWillSendRequest() if the client
request is null, since the load is going to be cancelled.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@176154 268f45cc-cd09-0410-ab3c-d52691b4dbfc