sequencer: break out of loop explicitly

It came up in review [1, 2] that this non-idiomatic loop is a bit tricky. When we find a space, we set `len = i`, which gives us the answer we are looking for, but which also breaks out of the loop. It turns out that this loop can confuse compilers as well. My copy of gcc 7.3.0 realizes that we are essentially evaluating `(len + 1) < len` and warns that the behavior is undefined if `len` is `INT_MAX`. (Because the assignment `len = i` is guaranteed to decrease `len`, such undefined behavior is not actually possible.) Rewrite the loop to a more idiomatic variant which doesn't muck with `len` in the loop body. That should help compilers and human readers figure out what is going on here. But do note that we need to update `len` since it is not only used just after this loop (where we could have used `i` directly), but also later in this function. While at it, reduce the scope of `i`. [1] https://public-inbox.org/git/CAPig+cQbG2s-LrAo9+7C7=dXifbWFJ3SzuNa-QePHDk7egK=jg@mail.gmail.com/ [2] https://public-inbox.org/git/CAPig+cRjU6niXpT2FrDWZ0x1HmGf1ojVZj3uk2qXEGe-S7i_HQ@mail.gmail.com/ Helped-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Martin Ågren <martin.agren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>