Add error message when SQL query failed

[nboisteault]

@rldhont @mdouchin
I think we should an error message for the user here.
I just had a case where an update query did not return $pkvals because some triggers avoided the update. Any suggestion?

lizmap-web-client/lizmap/modules/lizmap/controllers/edition.classic.php

Line 735 in 48c984e

// Redirect to the display action