Load GeoTIFF bands as colors when possible

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 70.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 93.78%. Comparing base (159d4ff) to head (02b8778).

Files	Patch %	Lines
src/extra/geotiff.jl	70.00%	9 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #111 +/- ## ========================================== - Coverage 94.53% 93.78% -0.75% ========================================== Files 18 18 Lines 1098 1111 +13 ========================================== + Hits 1038 1042 +4 - Misses 60 69 +9 ```

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