Fix fuzzer crash - validate host exists when user is specified

Co-authored-by: Byron <63622+Byron@users.noreply.github.com>

Author: Copilot

gix-url/src/simple_url.rs

@@ -82,6 +82,10 @@ impl<'a> ParsedUrl<'a> {
             };
 
             let (h, p) = Self::parse_host_port(host_port)?;
+            // If we have user info, we must have a host
+            if h.is_none() {
+                return Err(ParseError::InvalidDomainCharacter);
+            }
             (user, pass, h, p)
         } else {
             // No user info