Cancel quitting after answering No to a prompt

Currently tig quits even when we put "n" a prompt. However, this behaviour is not useful because, when a user cancels a command because of miss choosing, he may immediately want to retry the command with other (correct) commit/branch. The current behaviour forces users to relaunch tig and search the correct commit/branch from the top of history again.

This commit fixes the behaviour to do nothing when users choose "n" to a prompt.