Repair decoder undefined json bug

[dstallenberg]

When the stringified json contains a undefined or NaN value we need to replace it by null to allow for json.parse to work.
Previously we used a simple replace. Now its a regex that only replaces unquoted instances of undefined & NaN.

[coveralls]

Pull Request Test Coverage Report for Build 7167270278

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 46.9%

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Totals
Change from base Build 7166447209:	0.0%
Covered Lines:	1544
Relevant Lines:	3042

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💛 - Coveralls