backend/ninja: Fix bug in NinjaRule.length_estimate

The code would create a dictionary that was of type `str : list[str] |
str | None`. Then would later try to call `len(' '.join(dict[key]))`.
This would result in two different bugs:

 1. If the value is `None` it would except, since None isn't iterable
    and cannot be converted to a string
 2. If the value was a string, then it would double the length of the
    actual string and return that, by adding a space between each
    character

0 files changed, 0 insertions, 0 deletions