melib/src/email/address.rs: Fix invalid UTF8 panic

In StrBuilder::display there's an assumption that the string is valid utf-8 but if an email contains an invalid string inside the MIME encoded word part the conversion panics. Change it to a lossy UTF-8 conversion instead. Fixes #19

Reported-By: cycomanic

melib/src/email/address.rs

@@ -176,7 +176,7 @@ impl StrBuilder {
     pub fn display<'a>(&self, s: &'a [u8]) -> String {
         let offset = self.offset;
         let length = self.length;
-        String::from_utf8(s[offset..offset + length].to_vec()).unwrap()
+        String::from_utf8_lossy(&s[offset..offset + length]).to_string()
     }
 
     pub fn display_bytes<'a>(&self, b: &'a [u8]) -> &'a [u8] {