dbus-c++: Properly initialize and check file descriptors in DefaultMainLoop.

BUG=chromium:353524
TEST=dbus-c++ builds with latest Clang.

Change-Id: I3c8301f7676b404673eb9e60ca233c047da4dcb7
Reviewed-on: https://chromium-review.googlesource.com/190487
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Tested-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
4 files changed