Rule file picker does not submit selected file on "Enter" key press

[harolato]

After pressing "Enter" key in rule picker dialog window, corresponding rule file path does not appear in the "rule" field. Otherwise, after clicking on "ok" submit button in the rule picker window, path to the rule file appears correctly.

Steps to reproduce:

1. Open Motif transformation
2. Create any rule
3. Open rule editor dialog window
4. Click "..." to open rule picker window to choose rule file
5. Click on desired rule file to highlight it
6. Press "Enter" key
7. Rule picker window closes and "rule" field remains empty (untouched)