LibURL: Advance past the '@' delimiter after batch-parsing userinfo

After batch-processing the userinfo, the authority state advanced the
parse pointer onto the '@' and relied on the end-of-loop increment to
step past it. That increment uses the byte length of the authority's
first code point, not the delimiter's. When the first code point was
multi-byte, the pointer overshot into the middle of a code point and
the next iteration sliced the string at a non-char boundary causing the
process to panic. We now step past the delimiter explicitly so we don't
need to rely on the end of loop increment to do so.

Libraries/LibURL/Rust/src/url/parser.rs

@@ -671,8 +671,10 @@ pub(crate) fn basic_parse_into(
                         username_builder.push_str(&encoded_authority);
                     }
 
-                    // NB: Since we have batch processed the username/password, we need to move the pointer past those code points.
-                    pointer += authority_length;
+                    // NB: Since we have batch processed the username/password, we need to move the pointer past those
+                    //     code points and the U+0040 (@) delimiter.
+                    pointer += authority_length + '@'.len_utf8();
+                    continue;
                 }
                 // 2. Otherwise, if one of the following is true:
                 //    * c is the EOF code point, U+002F (/), U+003F (?), or U+0023 (#)

Tests/LibURL/TestURL.cpp

@@ -575,6 +575,25 @@ TEST_CASE(username_and_password)
     }
 }
 
+TEST_CASE(non_ascii_userinfo)
+{
+    {
+        auto url = URL::Parser::basic_parse("http://é@é"sv);
+        EXPECT(url.has_value());
+        EXPECT_EQ(url->username(), "%C3%A9"sv);
+        EXPECT(url->password().is_empty());
+        EXPECT_EQ(url->serialized_host(), "xn--9ca"sv);
+    }
+
+    {
+        auto url = URL::Parser::basic_parse("http://é@example.com"sv);
+        EXPECT(url.has_value());
+        EXPECT_EQ(url->username(), "%C3%A9"sv);
+        EXPECT(url->password().is_empty());
+        EXPECT_EQ(url->serialized_host(), "example.com"sv);
+    }
+}
+
 TEST_CASE(ascii_only_url)
 {
     {