Modify EditBox for win32

1. Do render when the system DialogBox popup
2. Star('*') wll be shown in win32 edit control if the EditBox's input flag is
password
3. Function editBoxTextChanged will be called when the text in win32
edit control is changed
4. The temporary variable (here is std::string) may destruct
when use expression like AnsiToUtf8(...).c_str() or Utf8ToAnsi(...).c_str()
I'm sorry than in function char* CWin32InputBox::AnsiToUtf8(const char* strAnsi) the local variable ret has not been initialized, and NULL should be assigned