[bug fix] quicksort was crashing for empty vector.
[bug fix] quicksort was crashing for empty vector.

fsrajer/yasfm,fsrajer/yasfm,fsrajer/yasfm,fsrajer/yasfm,fsrajer/yasfm,fsrajer/yasfm,fsrajer/yasfm,fsrajer/yasfm,fsrajer/yasfm,fsrajer/yasfm