Better handling for non-related keybindings

**Is your feature request related to a problem? Please describe.**
Like many others I have a set of keybindings related to other apps. Some of those keybindings are usually set to ``, in order to avoid conflicts with other applications, since It's very unusual to see that as a default anywhere. The problem is that when I'm at lazygit and hit `8` (bind to another app), lazygit closes immediately.

**Describe the solution you'd like**
I would like lazygit to bypass those commands, just like when hitting a single key that's not defined (e.g. pressing 'b' at the files pane).

**Describe alternatives you've considered**
I really don't know how It works or even if this is in the scope of lazygit, so I don't really have a solution in mind, but I figured I should bring It up, as I noticed that tig doesn't have this behavior.