Remove unnecessary Vector copy in mapHostName

https://bugs.webkit.org/show_bug.cgi?id=271440

Reviewed by Sihui Liu.

* Source/WTF/wtf/URLHelpers.cpp:
(WTF::URLHelpers::mapHostName):

Canonical link: https://commits.webkit.org/276638@main

Source/WTF/wtf/URLHelpers.cpp

@@ -651,7 +651,7 @@ std::optional<String> mapHostName(const String& hostName, URLDecodeFunction deco
     auto expectedSourceBuffer = string.charactersWithNullTermination();
     if (!expectedSourceBuffer)
         return std::nullopt;
-    auto sourceBuffer = expectedSourceBuffer.value();
+    auto sourceBuffer = expectedSourceBuffer->span();
 
     UChar destinationBuffer[URLParser::hostnameBufferLength];
     UErrorCode uerror = U_ZERO_ERROR;