undo-tree-load-history was formerly advised with doom*shut-up, which
uses the quiet! macro to suppress output. quiet! accomplishes this by
temporarily redefining message to a no-op function. However, if a fatal
error occurs while this binding is active, in some cases, message will
remain redefined, perpetually silencing all output to the minibuffer.
This tries to mitigate that, at least where undo-tree is concerned.
Also sharp-quotes an unquoted function.