use appender instead of array

Author: JackStouffer

std/utf.d

@@ -2470,8 +2470,15 @@ char[] toUTF8(return out char[4] buf, dchar c) nothrow @nogc @safe pure
  */
 string toUTF8(S)(S s) if (isSomeString!S)
 {
-    import std.array : array;
-    return s.byChar.array;
+    import std.array : appender;
+
+    auto app = appender!string();
+    app.reserve(s.length);
+
+    foreach (c; s.byChar)
+        app.put(c);
+
+    return app.data;
 }
 
 ///