Drop empty notes after editing.

Keeping empty notes doesn't make sense here. Also, there doesn't seem to
be a simple way to erase notes yet. This will make calcurse delete any
notes that are empty (meaning that they are either 0-byte files or
contain nothing but a newline character) when returning from the editor.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/day.c

@@ -1085,6 +1085,9 @@ day_edit_note (char *editor)
   (void)snprintf (fullname, BUFSIZ, "%s%s", path_notes, p->note);
   wins_launch_external (fullname, editor);
 
+  if (io_file_is_empty (fullname))
+    erase_note (&p->note, ERASE_FORCE);
+
   date = calendar_get_slctd_day_sec ();
   switch (p->type)
     {