webdav: OSL_ENSURE -> SAL_WARN_IF

Change-Id: I2940263bc8bdc739d5c591e19a6e4426afee3bb1
webdav: OSL_ASSERT -> assert

Change-Id: Ic6c7307aa9f8422816b9a335cbf3541c948026ce
webdav: OSL_TRACE -> SAL_INFO

Change-Id: Id5947de4c64e8128073f39c9a2871676f2a117ff