urlmon: Fix timing issue with FLAG_REQUEST_COMPLETE and InternetQueryDataAvailable in HttpProtocol_Continue.

wininet/tests: Test that for an open HTTP connection InternetQueryDataAvailable succeeds or returns ERROR_IO_PENDING.

wininet: InternetQueryDataAvailable does not return ERROR_NO_MORE_FILES when no more HTTP data is available.

winex11.drv: Correctly handle overlapping source and destination regions on the same DIB when copying DIBs client-side.