Avoid MSVC iterator debugging assertion

Summary:
When compiling with MSVC STL headers and iterator debugging enabled
(a common case for debug builds), attempting to dereference
std::string::end() leads to a failing assertion.

To avoid this, we can just use the data pointer and string size to
fetch the begin and end addressed of the string.

Reviewed By: neildhar

Differential Revision: D66009100

fbshipit-source-id: cac2b796be4973db6811b08a2e696c8df7ec85d6

lib/VM/JSError.cpp

@@ -755,8 +755,8 @@ void JSError::appendBytecodeFrame(
             location->filenameId);
     convertUTF8WithSurrogatesToUTF16(
         std::back_inserter(stack),
-        &*utf8Filename.begin(),
-        &*utf8Filename.end());
+        utf8Filename.data(),
+        utf8Filename.data() + utf8Filename.size());
   } else {
     auto sourceURL = runtimeModule->getSourceURL();
     stack.append(sourceURL.empty() ? "unknown" : sourceURL);