Remove the exclusion between '?' and internal command

[liangkarl]

According to the document, '?' have the top priority while running external command, but it will fail if the keybind is like this bind main pc :?!git log which is a legal combination.

In this commit, I simply move the confirm check to the first place.

External user-defined command
    These actions start with one or more of the following option flags followed by the command that should be executed.
    !   Run the command in the foreground with output shown.
    @   Run the command in the background with no output.
    +   Run the command synchronously, and echo the first line of
        output to the status bar.
    ?   Prompt the user before executing the command.
    <   Exit Tig after executing the command.
    >   Re-open Tig instantly in the last displayed view after
        executing the command.