Fix FromForm without WithOpenApi schemas

[jgarciadelanoceda]

Fixes #3126.
Also I have found that there was an error for WithOpenApi for FromFormParameters that are enums

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.55%. Comparing base (0554326) to head (ec2e87f).
Report is 3 commits behind head on master.

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@@            Coverage Diff             @@
##           master    #3133      +/-   ##
==========================================
+ Coverage   91.44%   91.55%   +0.10%     
==========================================
  Files          76       76              
  Lines        3121     3125       +4     
  Branches      520      526       +6     
==========================================
+ Hits         2854     2861       +7     
+ Misses        267      264       -3     

Flag	Coverage Δ
Linux	81.90% <98.30%> (+0.05%)	⬆️
Windows	91.55% <100.00%> (+0.10%)	⬆️
macOS	91.55% <100.00%> (+0.10%)	⬆️

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[martincostello]

Thanks - will merge this after #3007.

[jgarciadelanoceda]

We may need to create an issue to check the order of filters to avoid this behaviour but I applied here.. I can remove it if you like and address it on other PR.. But I did not know why the Description did not show up. First filter wins?

[martincostello]

First filter wins?

Probably. I did similar things in my new OpenAPI extensions NuGet package to not overwrite things in the OpenAPI document if they already had a value.