When displaying Chinese help information, the program does not respond. The code enters a dead loop.

[赵伟]

When displaying Chinese help information, the program does not respond. 
The code enters a dead loop in file "libgetopt++/include/getopt++/DefaultFormatter.h"，Because some Chinese help information does not contain spaces.
diff --git a/libgetopt++/include/getopt++/DefaultFormatter.h b/libgetopt++/include/getopt++/DefaultFormatter.h
index ee2397f5..19ac67e1 100644
--- a/libgetopt++/include/getopt++/DefaultFormatter.h
+++ b/libgetopt++/include/getopt++/DefaultFormatter.h
@@ -64,6 +64,7 @@ class DefaultFormatter {
        {
          // TODO: consider using a line breaking strategy here.
          int pos = helpmsg.substr(0,h_len).find_last_of(" ");
+         if(pos<=0)break;
          theStream << helpmsg.substr(0,pos)
                    << std::endl << std::string (o_len, ' ');
          helpmsg.erase (0,pos+1);