A string can parse as a non-zero double that's smaller than the
smallest float yet be a faithful representation of the smallest float.
So rather than testing for non-zero doubles less than the smallest
float, test for non-zero doubles that cast to float zero; these
underflow. This means small values close below the smallest float
shall round up to it, rather than down to zero, requiring a tweak to
an existing test. Added a test for the boundary case (and tidied the
test data).
Fixes: QTBUG-74833
Change-Id: I4cb30b3c0e54683574b98253505607caaf88fbfb
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
954b73445c