Smith-Waterman dialog crashes on custom region selected

It crashes on two scenarios:

1. Opened the Smith-Waterman dialog.
2. Selected "Custom" (there was only "Whole sequence" and "Custom" values).
3. Clicked the "Search" button.
=> After a second or two the crash occurred.

and

1. Opened the Smith-Waterman dialog.
2. Enter custom region 1..2
3. Enter patter "ACGT"
4. Click the "Search" button and it crashes.

Along with the crash fixing, when a pattern length longer than a selected region a warning must be shown.