fix dn4000 bug

[moustakas]

Fix #131.

[github-actions[bot]]

Pull Request Test Coverage Report for Build 5656415013

• 6 of 7 (85.71%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage remained the same at 50.349%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
py/fastspecfit/fastspecfit.py	2	3	66.67%
<!--	Total:	6	7	85.71%	-->

Files with Coverage Reduction	New Missed Lines	%
py/fastspecfit/fastspecfit.py	1	13.27%
<!--	Total:	1		-->

Totals
Change from base Build 5587007847:	0.0%
Covered Lines:	2235
Relevant Lines:	4439

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💛 - Coveralls

[moustakas]

To make sure I fixed the problem---and didn't introduce any new ones!---I ran about ~4000 BGS galaxies on tile 80613 through this branch and compared them with the Fuji/v2.0 VAC. (In retrospect, I should have used an LRG tile, but oh well.)

This figure clearly shows that the issue has been addressed.