Removed "#define nullptr" since it can cause compile errors.

nullptr is a keyword. If some compiler doesn't have nullptr, it would
be better to define nullptr for that compiler specifically.
Fixed superfluous scrollbar change events.

Adjust invalid max to min instead of the reverse since it's a much
more common use case that min is 0 and max is calculated.

TBEditField calculates a negative max when scrollbars aren't needed
which changed both min and value each time, causing change events.