NewPositiveDecimalFromStrings expects error when value is NaN

[ryanchristo]

Summary of Bug

Intermittent error in CI when testing NewPositiveDecFromString.

Any form of "NaN" ("NAn", "nAn", etc) doesn't error but the tests expect an error.

https://github.com/regen-network/regen-ledger/runs/6802813188?check_suite_focus=true#step:5:840

=== RUN   TestDec/TestInvalidNewPositiveDecFromString
    dec_test.go:23: [rapid] failed after 8 tests: (*T).FailNow() called
        To reproduce, specify -run="TestDec/TestInvalidNewPositiveDecFromString" -rapid.failfile="TestDec_TestInvalidNewPositiveDecFromString-20220608223342-42708.fail" (or -rapid.seed=3401434366935564329)
        Failed test output:
    dec_test.go:229: [rapid] draw s: "NAn"
    dec_test.go:231: 
        	Error Trace:	dec_test.go:231
        	            				engine.go:276
        	            				engine.go:158
        	            				engine.go:115
        	Error:      	An error is expected but got nil.
        	Test:       	TestDec/TestInvalidNewPositiveDecFromString

Version

master

Steps to Reproduce

Pass "NaN" to NewPositiveDecFromString without receiving an error.

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For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned

[ryanchristo]

https://github.com/regen-network/regen-ledger/runs/6973388255?check_suite_focus=true#step:5:1147

[ryanchristo]

https://github.com/regen-network/regen-ledger/runs/7043642886?check_suite_focus=true#step:4:1207