Potential memory leak when adding phrase to phrase book is aborted

In mainwindow.cpp, MainWindow::adToPhraseBook, a new Phrase is allocated on the heap. If later on the QMessageBox::information("Add to phrase book", ...) confirmation is canceled, then 'phrase' is not added to the hash, and the pointer variable goes out of scope without being deleted.

Coverity issue: https://scan3.coverity.com/reports.htm#v42553/p10113/fileInstanceId=32688635&defectInstanceId=8978285&mergedDefectId=22122