global: Do not assert >= 0 for unsigned values

global: Do not assert >= 0 for unsigned values

Unsigned values are always >= 0. These assertions are redundant, so remove them.

$ grep assert -r ./ |grep ">=" |grep 0
shows the assert(something >= 0). Remove those which assert(unsigned >= 0).

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>