Correct form name to smtp_email to fix matching in InstallForm struct.

templates/install.tmpl

@@ -123,8 +123,8 @@
                 <span class="help">{{.i18n.Tr "install.smtp_from_helper"}}</span>
               </div>
               <div class="inline field {{if .Err_SMTPEmail}}error{{end}}">
-                <label for="smtp_user">{{.i18n.Tr "install.mailer_user"}}</label>
+                <label for="smtp_email">{{.i18n.Tr "install.mailer_user"}}</label>
-                <input id="smtp_user" name="smtp_user" value="{{.smtp_user}}">
+                <input id="smtp_email" name="smtp_email" value="{{.smtp_email}}">
               </div>
               <div class="inline field">
                 <label for="smtp_passwd">{{.i18n.Tr "install.mailer_password"}}</label>