UGENE GUI freezing on annotation of all restriction sites

The issue was reproduced on a user's notebook (see the "Environment" field).

The user opened a common plasmid with the Circular View and searched for all restriction sites at the same time. The result was that the UGENE GUI freezed.

Do the following:

1. Make sure the auto-annotating task does not start several times, when the previous one is running (there were 3 tasks, when he clicked 3 times).
2. Optimize the searching/visualization of the sites. The sites may be searched in the background, but UGENE should not freeze the main window.