WebPositive crash if authentication dialog is cancelled

[rhester72]

Discovered this while trying to understand why ​http://haikuware.com seems hopelessly broken, requiring authentication for every page.

If you cancel the authentication dialog enough times, WebPositive will eventually give up the ghost.

Backtrace:

#0  0x00a6b4b8 in WebCore::ResourceHandle::didReceiveAuthenticationChallenge ()
   from /boot/apps/WebPositive/lib/libwebcore.so
#1  0x00a72d33 in _ZN7WebCoreL24handleHTTPAuthenticationEPNS_14ResourceHandleE
    () from /boot/apps/WebPositive/lib/libwebcore.so
#2  0x00a7376d in WebCore::ResourceHandleManager::downloadTimerCallback ()
   from /boot/apps/WebPositive/lib/libwebcore.so
#3  0x00a738d0 in WebCore::Timer<WebCore::ResourceHandleManager>::fired ()
   from /boot/apps/WebPositive/lib/libwebcore.so
#4  0x00a1070b in WebCore::ThreadTimers::sharedTimerFiredInternal ()
   from /boot/apps/WebPositive/lib/libwebcore.so
#5  0x00a10769 in WebCore::ThreadTimers::sharedTimerFired ()
   from /boot/apps/WebPositive/lib/libwebcore.so
#6  0x00a4d188 in WebCore::SharedTimerHaiku::MessageReceived ()
   from /boot/apps/WebPositive/lib/libwebcore.so
#7  0x027aeaa8 in BLooper::DispatchMessage ()
   from /boot/system/lib/gcc4/libbe.so
#8  0x027a5913 in BApplication::DispatchMessage ()
   from /boot/system/lib/gcc4/libbe.so
#9  0x027b05e4 in BLooper::task_looper () from /boot/system/lib/gcc4/libbe.so
#10 0x027a61d4 in BApplication::Run () from /boot/system/lib/gcc4/libbe.so
#11 0x0023b233 in main ()

If any other debug information is required, please advise. This is 100% reproducible.