fix ignore walking on form mapping (#1942)

[vkd]

Now the ignore tag form"-" not allow for the mapping to walk inside that field.
Fix #1942

[codecov]

Codecov Report

Merging #1943 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1943   +/-   ##
=======================================
  Coverage   98.74%   98.74%           
=======================================
  Files          40       40           
  Lines        2236     2236           
=======================================
  Hits         2208     2208           
  Misses         14       14           
  Partials       14       14

Impacted Files	Coverage Δ
binding/form_mapping.go	100% <100%> (ø)	⬆️

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[thinkerou]

@vkd thanks! may it break backward?

[vkd]

Yes, but only in unusual and undocumented cases like this:

type A struct {
	Name string `form:"name"`
}
type S struct {
	A A `form:"-"`
}

var s S
req, _ := http.NewRequest("GET", "/?name=mike", nil)
err := Form.Bind(req, &s)
// s.A.Name == ""
// s.A.Name != "mike"

In my mind (and as I can see by this case: #1942 (comment)), the new way to ignore the whole inner struct by tag form:"-" is more obvious.

[vkd]

Let's try to restart the build in the TravisCI.
For me it works.