[PATCH] fix -Wsign-compare error in objc-act.c (PR objc/50743)

[Nicola Pero]

> (I don't have svn write access so I'll need someone else to commit it if
> it's approved.)

I can apply it for you.  But ... do you have a copyright assignment in place
for contributions to GCC ?  The patch looks small and trivial enough that
I think I can apply it without a signed copyright assignment form, but if you
plan on contributing more, it would make sense to sign one. :-)

Thanks