Only set the user password if the password field would have been shown (#12980)

POSTing to /admin/users/:id should only set the password if the the user
IsLocal or IsOauth2

Fix #12952

Signed-off-by: Andrew Thornton <art27@cantab.net>

routers/admin/users.go

@@ -224,7 +224,7 @@ func EditUserPost(ctx *context.Context, form auth.AdminEditUserForm) {
 		}
 	}
 
-	if len(form.Password) > 0 {
+	if len(form.Password) > 0 && (u.IsLocal() || u.IsOAuth2()) {
 		var err error
 		if len(form.Password) < setting.MinPasswordLength {
 			ctx.Data["Err_Password"] = true