fastuidraw/painter/painter_brush: bug fix for computing max-mipmap-level.
fastuidraw/painter/painter_brush: bug fix for computing max-mipmap-level.

Sighs, an off by one counting bug snuck in. The max mipmap level allowed
is one less than the number of mipmap levels, because the counting starts
at zero.

01org/fastuidraw,01org/fastuidraw