Fix form binding with json custom type that underling form is string(#2510)

[LaysDragon]

What it solves

Current form binding will failed if custom struct type that underling is string with json.Unmarshal . detail see #2510
It will trying to Unmarshal the value with quoted again to fix this issue.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.46%. Comparing base (540b1ef) to head (e425b26).
Report is 385 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2511   +/-   ##
=======================================
  Coverage   98.45%   98.46%           
=======================================
  Files          41       41           
  Lines        1948     1952    +4     
=======================================
+ Hits         1918     1922    +4     
  Misses         17       17           
  Partials       13       13           

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[thinkerou]

@LaysDragon thanks, please add unit test.

[LaysDragon]

ok,I add it. And wrap two error together if second time try parse still failed.
well that the problem go 1.11 doesn't have error wrap...

[LaysDragon]

@LaysDragon thanks, please add unit test.
ok it done

[eloyekunle]

Any update on this?