Issue 5216 - [emscripten] Use a more reliable way of retrieving mangled function name

compiled/bindings/library.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 "use strict";
 
 mergeInto(LibraryManager.library, {
   GetFunctionName__asm: true,
   GetFunctionName__sig: [],
   GetFunctionName: function(buffer, ptr, signature)
   {
     var table = eval("FUNCTION_TABLE_" + AsciiToString(signature));
     var name = table[HEAP32[ptr >> 2] % table.length].name;
     if (buffer)
-      stringToAscii(name, buffer);
-    return name.length + 1;
+      writeAsciiToMemory(name, buffer, true);
+    return name.length;
   }
 });