Show error once

Show error string only once when deleting a non-existent record by index.

E.g.:

    buku -d non_existent_id

Fix indentation issue.

buku.py

@@ -1362,6 +1362,12 @@ class BukuDb:
         else:  # Remove a single entry
             try:
                 if self.chatty:
+                    self.cur.execute('SELECT COUNT(*) FROM bookmarks WHERE id = ? LIMIT 1', (index,))
+                    count = self.cur.fetchone()
+                    if (count[0] < 1):
+                        logerr('No matching index %d', index)
+                        return False
+
                     if self.print_rec(index) is True:
                         resp = input('Delete this bookmark? (y/n): ')
                         if resp != 'y':