Problems with displaying long option description with cyrillic characters

I'm having some weird issues with displaying long option description that contains cyrillic characters:

```
[program_options]$ ./example --help
Allowed options:
-h [ --help ] print usage message
-f [ --enforcewrite ] enforcewrite Всегда перезаписывать
файлы в директории с
преобразованной
политикой безопасност▒
▒
```
Note that weird symbols at the description end.
Here's the code to reproduce it:

```
#include
using namespace boost::program_options;

#include
using namespace std;

int main(int argc, char* argv[])
{
string s;

options_description desc("Allowed options");
desc.add_options()
("help,h", "print usage message")
("enforcewrite,f", value(&s)->value_name("enforcewrite"),
"Всегда перезаписывать файлы в директории с преобразованной политикой безопасности");

variables_map vm;
store(parse_command_line(argc, argv, desc), vm);

if (vm.count("help")) {
cout << desc << "\n";
return 0;
}
}
```

Appearance of such symbols seems to depend somehow on the length of the text string associated with the option (including option name, default value and it's description). In my case I worked around the problem by increasing the column width.

program option version is: 1.62.0
OS: CentOS 7.1

Start with the options_description help output and the add_options call shown in the reproducer, then run the example with the long Cyrillic description. Trace how the streamed help text wraps the option and check that the output ends without replacement symbols when the column width is unchanged. The workaround of increasing the column width provides a comparison case.

索引モデルが issue の本文から書いたものです。