[glibmm] Glib::ustring fix gcc 6 warning in public header

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 07461be382cb5760505cd7d6fc985941491d8bf2
Author: Aurelien Jacobs <aurel gnuage org>
Date:   Mon Jan 18 14:39:12 2016 +0100

    Glib::ustring fix gcc 6 warning in public header
    
    Avoid a warning when compiling with gcc 6 with -Wmisleading-indentation.
    Bug #760641.

 glib/glibmm/ustring.h |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/glib/glibmm/ustring.h b/glib/glibmm/ustring.h
index 528a536..ccbb103 100644
--- a/glib/glibmm/ustring.h
+++ b/glib/glibmm/ustring.h
@@ -1004,7 +1004,8 @@ const ustring_Iterator<T> ustring_Iterator<T>::operator++(int)
 template <class T> inline
 ustring_Iterator<T>& ustring_Iterator<T>::operator--()
 {
-  do --pos_; while((static_cast<unsigned char>(*pos_) & 0xC0u) == 0x80);
+  while ((static_cast<unsigned char>(*--pos_) & 0xC0u) == 0x80)
+    ;
   return *this;
 }