Long commit messages are not truncated within dialog screen

Long commit messages scroll off of the available dialogue windows instead of being truncated to fit.

TO reproduce:
1. Create repository
2. Make any changes
3. Commit with long message (any long message, 'lorem ipsum ...' will be good). It can be singl eline message or multiline, no matter.
4. Make other changes and commit it with any message.
5. Select first commit, open context menu and call "Reset master to this commit"
6. You will see window, that appears on top of program (see screenshot). It may be so wide, wider than your screen.