Fix issue with too small season length (#2780)

[deniszh]

Fixing #2780

[codecov-commenter]

Codecov Report

Base: 76.34% // Head: 76.32% // Decreases project coverage by -0.01% :warning:

Coverage data is based on head (bd1320e) compared to base (2f178f4). Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2787 +/- ## ========================================== - Coverage 76.34% 76.32% -0.02% ========================================== Files 88 88 Lines 9667 9669 +2 Branches 2060 2061 +1 ========================================== Hits 7380 7380 - Misses 2020 2021 +1 - Partials 267 268 +1 ``` | [Impacted Files](https://codecov.io/gh/graphite-project/graphite-web/pull/2787?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=graphite-project) | Coverage Δ | | |---|---|---| | [webapp/graphite/render/functions.py](https://codecov.io/gh/graphite-project/graphite-web/pull/2787/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=graphite-project#diff-d2ViYXBwL2dyYXBoaXRlL3JlbmRlci9mdW5jdGlvbnMucHk=) | `94.94% <0.00%> (-0.09%)` | :arrow_down: | | [webapp/graphite/tags/redis.py](https://codecov.io/gh/graphite-project/graphite-web/pull/2787/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=graphite-project#diff-d2ViYXBwL2dyYXBoaXRlL3RhZ3MvcmVkaXMucHk=) | `87.03% <0.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=graphite-project). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=graphite-project)

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[deniszh]

💚 All backports created successfully

Status	Branch	Result
✅	1.1.x

Questions ?

Please refer to the Backport tool documentation