set a default exit code in main
set a default exit code in main

If we ever fail the command, set a default error code (EINVAL, 22) so
that we never return success in such case.

Signed-off-by: Peng Tao <39d8af57313740070ea49547576f55682fe5221a@gmail.com>

gnawux/runv,bergwolf/runv,gao-feng/runv,gao-feng/runv,laijs/runv,bergwolf/runv,laijs/runv,jinfenw/runv,jinfenw/runv,bergwolf/runv,hyperhq/runv,hyperhq/runv,gnawux/runv,gao-feng/runv,hyperhq/runv,gnawux/runv,laijs/runv,jinfenw/runv