8026300: VM warning: increase O_BUFLEN in ostream.hpp -- output truncated...

8026300: VM warning: increase O_BUFLEN in ostream.hpp -- output truncated occurs with fastdebug VM when printing flags
Summary: Fixed wrong print string format
Reviewed-by: sla, ccheung

src/share/vm/runtime/globals.cpp

@@ -325,7 +325,7 @@ void Flag::print_on(outputStream* st, bool withComments) {
     else st->print("%-16s", "");
   }
 
-  st->print("%-20");
+  st->print("%-20s", " ");
   print_kind(st);
 
   if (withComments) {