cli: error when searching for NUL

Basically, unless the -a/--text flag is given, it is generally always an
error to search for an explicit NUL byte because the binary detection
will prevent it from matching.

Fixes #1838

crates/regex/src/lib.rs

@@ -9,6 +9,7 @@ pub use crate::{
 };
 
 mod ast;
+mod ban;
 mod config;
 mod error;
 mod literal;