Handle error when contour coordinates contain NaN or inf, #149

[coveralls]

Pull Request Test Coverage Report for Build 574

• 14 of 19 (73.68%) changed or added relevant lines in 2 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.04%) to 84.128%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
contour/views.py	6	8	75.0%
contour/validators.py	8	11	72.73%
<!--	Total:	14	19	73.68%	-->

Files with Coverage Reduction	New Missed Lines	%
contour/views.py	1	79.02%
<!--	Total:	1		-->

Totals
Change from base Build 570:	-0.04%
Covered Lines:	1394
Relevant Lines:	1657

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💛 - Coveralls