net/http: multipart ReadForm close file after copy
net/http: multipart ReadForm close file after copy

Always close the file regardless of whether the copy succeeds or fails.
Pass along the close error if the copy succeeds

Fixes #16296

Change-Id: Ib394655b91d25750f029f17b3846d985f673fb50
Reviewed-on: https://go-review.googlesource.com/30410
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

vsekhar/elastic-go,suncycheng/go,derekmarcotte/go,derekmarcotte/go,derekmarcotte/go,goodlang/good,Cofyc/go,akutz/go,josharian/go,nawawi/go,codestation/go,polyverse-security/go,suncycheng/go,ImJasonH/go,ImJasonH/go,suncycheng/go,Cofyc/go,vsekhar/elastic-go,golang/go,Cofyc/go,goodlang/good,linux-on-ibm-z/go,josharian/go,polyverse-security/go,suncycheng/go,cloudflare/go,derekmarcotte/go,akutz/go,josharian/go,momchil-velikov/go,goodlang/good,polyverse-security/go,cloudflare/go,nawawi/go,codestation/go,suncycheng/go,josharian/go,vsekhar/elastic-go,CAFxX/go,suncycheng/go,ImJasonH/go,momchil-velikov/go,nawawi/go,golang/go,Cofyc/go,derekmarcotte/go,cloudflare/go,derekmarcotte/go,momchil-velikov/go,golang/go,codestation/go,CAFxX/go,josharian/go,vsekhar/elastic-go,akutz/go,goodlang/good,nawawi/go,josharian/go,akutz/go,linux-on-ibm-z/go,cloudflare/go,akutz/go,Cofyc/go,codestation/go,akutz/go,golang/go,goodlang/good,Cofyc/go,linux-on-ibm-z/go,derekmarcotte/go,polyverse-security/go,cloudflare/go,vsekhar/elastic-go,polyverse-security/go,golang/go,codestation/go,golang/go,goodlang/good,polyverse-security/go,cloudflare/go,golang/go,suncycheng/go,josharian/go,vsekhar/elastic-go,momchil-velikov/go,derekmarcotte/go,Cofyc/go,linux-on-ibm-z/go,vsekhar/elastic-go,ImJasonH/go,akutz/go,CAFxX/go,cloudflare/go,goodlang/good,ImJasonH/go,CAFxX/go,codestation/go,momchil-velikov/go,josharian/go,CAFxX/go,christopher-henderson/Go,akutz/go,Cofyc/go,CAFxX/go,linux-on-ibm-z/go,nawawi/go,cloudflare/go,linux-on-ibm-z/go,nawawi/go,momchil-velikov/go,CAFxX/go,nawawi/go,polyverse-security/go,momchil-velikov/go,CAFxX/go,codestation/go,momchil-velikov/go,goodlang/good,polyverse-security/go,ImJasonH/go,linux-on-ibm-z/go,suncycheng/go,codestation/go,ImJasonH/go,golang/go,vsekhar/elastic-go,nawawi/go,linux-on-ibm-z/go,ImJasonH/go