Fix org contact email not clearable once set (#36975)

When the email field was submitted as empty in org settings (web and
API), the previous guard `if form.Email != ""` silently skipped the
update, making it impossible to remove a contact email after it was set.

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Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

templates/swagger/v1_json.tmpl

@@ -24855,7 +24855,7 @@
           "x-go-name": "Description"
         },
         "email": {
-          "description": "The email address of the organization",
+          "description": "The email address of the organization; use empty string to clear",
           "type": "string",
           "x-go-name": "Email"
         },