fixes #2001

[piliugin-anton]

fixes #2001

What issue does this pull request resolve? https://github.com/ajv-validator/ajv/issues/2001 What changes did you make? Added if condition to check whether property is first Is there anything that requires more attention while reviewing? Code correctness

[epoberezkin]

@piliugin-anton thank you!

It needs the test that fails without this change.

[piliugin-anton]

@epoberezkin should I write a test or you will do it?

[epoberezkin]

@piliugin-anton it's great if you can - probably should be something similar to this one: https://github.com/ajv-validator/ajv/blob/master/spec/issues/1501_jtd_many_properties.spec.ts

[piliugin-anton]

@epoberezkin Okay, I will try. Will push the changes in an hour and ping you

[piliugin-anton]

@epoberezkin How do I write a test, when I already have a changes that returns correct result of serialization. Could you please assist me?

[piliugin-anton]

@epoberezkin Please check if test is correct

[epoberezkin]

amended in #2190