Issue/1448 Fix showing NaN in date time x-axis when disabled legends in multi series line chart with straight line

[cola119]

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Fixes #1448

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
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• I have added tests that prove my fix is effective or that my feature works
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