Clean fix dtype checking in local plotting

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.30% :tada:

Comparison is base (172f57d) 79.12% compared to head (ab5ef75) 79.42%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #220 +/- ## ========================================== + Coverage 79.12% 79.42% +0.30% ========================================== Files 89 89 Lines 7893 7894 +1 ========================================== + Hits 6245 6270 +25 + Misses 1648 1624 -24 ``` | [Files Changed](https://app.codecov.io/gh/YosefLab/Cassiopeia/pull/220?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=YosefLab) | Coverage Δ | | |---|---|---| | [cassiopeia/plotting/local.py](https://app.codecov.io/gh/YosefLab/Cassiopeia/pull/220?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=YosefLab#diff-Y2Fzc2lvcGVpYS9wbG90dGluZy9sb2NhbC5weQ==) | `89.96% <100.00%> (+9.34%)` | :arrow_up: |

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