Revert "Core: Don't wait for completion if cancel_transfer failed"

This reverts commit 2f5023c41d3176e56bf0abc521b7c5f8b1ac4664. 2f5023c4
was an attempt to fix: https://github.com/libusbx/libusbx/issues/76

As seen in: http://libusbx.1081486.n5.nabble.com/Libusbx-devel-libusb-interrupt-transfer-does-not-return-in-case-of-error-td626.html

[372849.680990] [0000275b] libusbx: error [reap_for_handle] reap failed error -1 errno=14
[372849.681752] [0000275b] libusbx: error [handle_events] backend handle_events failed with error -1
[372850.680466] [0000275b] libusbx: warning [handle_timeout] async cancel failed -5 errno=22

The problem begins with reap_for_handle failing with errno == 14, which is
EFAULT. So the real problem is the application passing in an invalid (or too
short) buffer, and thus is an application bug.

The fix masks this problem, but causes the problem of calling
libusb_transfer_free() on a non finished transfer, so it is no good.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>

Conflicts:
	AUTHORS
	libusb/version_nano.h
sync.c: Do not free an incompleted transfer

Before this patch the code in sync.c would free an incomplete transfer
when libusb_handle_events_completed exits with an error twice in a row.

But we should never free an incomplete transfer, otherwise we may end up
referencing free-ed memory later on.

This patch simply logs an error and keeps on trying until the transfer
completes.

Note that if libusb_handle_events_completed keeps throwing an error the
entire time, without ever completing the transfer, this patch effectively
replaces a potential crash / unspecified behavior, with an endless loop
and logging a ton of errors making clear what is going on.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
sync.c: Remove code duplication

Signed-off-by: Hans de Goede <hdegoede@redhat.com>