QDebugStateSaver: call maybeSpace() in destructor.

tst_qdebug didn't test adding something else after the MyLine object,
so I didn't realize that a space was missing there. All debug operators
should end with maybeSpace(), but with the settings of the caller, so this
requires restoring the settings before calling it. To make it convenient
for all << operators, the destructor of QDebugStateSaver takes care of that.

Change-Id: I18ab78d99d7ee3be951082b5b5d34718ee60e21d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>