MythUIScrollBar: Initialize maximum to zero until it is actually known,
otherwise the scrollbar is drawn prematurely.

(cherry picked from commit 899f3d3185c994715c86cd42bf56e011266e4c9c)
MythMainWindow::Norm: With very small values of x, scaling down can cause
the 'normalized' value to go to zero.  Rounding the result fixes this, and
is probably more desireable anyway.

(cherry picked from commit 42bae47be8794eac2dadff3b4fd1a7fa3c547b82)