Fix a data corruption issue in custom query editor (fixes #2113)
Fix a data corruption issue in custom query editor (fixes #2113)

... which occurred if ALL of the following conditions were met:
* A cell of a custom query result was being edited
* At the same time another process removed said row
* The custom query was rerun without canceling or finishing the edit first
(also added a NSBeep() for a certain tooltip error message)

josegonzalez/sequelpro,eric-seekas/sequelpro,eric-seekas/sequelpro,CoolSwitcher/sequelpro,abhibeckert/sequelpro,dnl-jst/sequelpro,leichunxin/sequelpro,kaneshin/sequelpro,Jellyfrog/sequelpro,dnl-jst/sequelpro,treejames/sequelpro,treejames/sequelpro,eric-seekas/sequelpro,CoolSwitcher/sequelpro,eric-seekas/sequelpro,abhibeckert/sequelpro,Jellyfrog/sequelpro,CoolSwitcher/sequelpro,kaneshin/sequelpro,chenbk85/sequelpro,dnl-jst/sequelpro,CoolSwitcher/sequelpro,Jellyfrog/sequelpro,abhibeckert/sequelpro,josegonzalez/sequelpro,josegonzalez/sequelpro,kaneshin/sequelpro,chenbk85/sequelpro,chenbk85/sequelpro,dnl-jst/sequelpro,treejames/sequelpro,kaneshin/sequelpro,treejames/sequelpro,leichunxin/sequelpro,Jellyfrog/sequelpro,leichunxin/sequelpro,chenbk85/sequelpro,josegonzalez/sequelpro,leichunxin/sequelpro,abhibeckert/sequelpro