Display non printable ascii chars with a dark dot (#580)

* Display non printable ascii chars with a dark dot

* Revert into_iter

src/usr/hex.rs

@@ -33,7 +33,9 @@ pub fn print_hex(buf: &[u8]) {
 }
 
 pub fn print_hex_at(buf: &[u8], offset: usize) {
+    let null = 0 as char;
     let cyan = Style::color("LightCyan");
+    let gray = Style::color("DarkGray");
     let pink = Style::color("Pink");
     let reset = Style::reset();
 
@@ -50,11 +52,13 @@ pub fn print_hex_at(buf: &[u8], offset: usize) {
             if *byte >= 32 && *byte <= 126 {
                 *byte as char
             } else {
-                '.'
+                null
             }
         ).collect();
 
-        println!("{}{:08X}: {}{:40}{}{}", cyan, addr, pink, hex, reset, ascii);
+        let text = ascii.replace(null, &format!("{}.{}", gray, reset));
+
+        println!("{}{:08X}: {}{:40}{}{}", cyan, addr, pink, hex, reset, text);
     }
 }