Crash if Cancel task of building Sitecone model

 Very old bug, this crash may have existed prior to v1.19.

Scenario:

1. Open Tools->Search for TFBS ->Build SITECON model menu item
2. SITECON build dialog appears
3. Set Input alignment in _common_data/clustal/1000_sequences.aln
4. Set any name in the Output model
5. Click Build button
   Expected: Build button transformed in Hide button
   Some info appears in the Status line
6. Wait 15 seconds and click Cancel button
   Crash
   Assertion failed: origMatrix.size() == settings.windowSize - 1, file D:\ugene\ugene\src\plugins_3rdparty\sitecon\src\SiteconAlgorithm.cpp, line 357
   Canceling task: Build SITECON model