The rule-of-thumb the FSF uses is `if the fix is trivial, no assignment is required: things ten lines long or less are assumed trivial'.
It looks like you slipped in just above that limit.
(I find it very little effort to do the occasional copyright assignment dance: the *really* annoying part is getting your employer to disclaimer-of-rights forms, because even if they agree they can be *so* damn slow at it it's not true. I've had to wait >6mths for these sometimes.)
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