Fix QSPI::isNull()

The method QSPI::isNull() should return false when QSPI is empty.

Tested on Winsows 8 and Linux with on-board, virtual and USB serial
ports using Qt5 and then Qt4.

Task-number: QTBUG-41262
Change-Id: Ic9e0afc5549311283aef7ec2ed841f5e418b7edf
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>
Declare QElapsedTimer closer to usage

Change-Id: I74622eaf3a7f5179ff25fc815997d5e4cf3cc2c7
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>
Simplify handling of overlapped result

There is not necessary to pass direction to handleOverlappedResult().
Because it is passed already as a second argument (pointer to
OVERLAPPED structure that defines a desired direction).

Also this method is renamed to more simple and short name.

Change-Id: I9c20cf97c1712aed8d3e9ea6d9b4687ce4487523
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>
Remove the 'register' keyword

It doesn't do anything and has been deprecated in C++14. Clang even
prints a warning.

Change-Id: Ie803a206f02897f99358ed22bf9cb999ca457741
Reviewed-by: Denis Shienkov <denis.shienkov@gmail.com>
Remove Q_OS_WIN64 since Q_OS_WIN32 defines 64-bit too

Change-Id: I32eaf132f19a3b6fcbd5fd55d0690c3bd62bb641
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>