[libsigcplusplus] Use {} with multiline while() blocks.

[Murray Cumming <murrayc src gnome org>]

commit e68e73079056411ee8cc4344e898385263930ed2
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Mar 31 15:25:38 2016 +0200

    Use {} with multiline while() blocks.

 sigc++/signal_base.cc |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/sigc++/signal_base.cc b/sigc++/signal_base.cc
index 254a90f..a16490f 100644
--- a/sigc++/signal_base.cc
+++ b/sigc++/signal_base.cc
@@ -168,10 +168,12 @@ signal_impl::sweep()
   deferred_ = false;
   auto i = slots_.begin();
   while (i != slots_.end())
+  {
     if ((*i).empty())
       i = slots_.erase(i);
     else
       ++i;
+  }
 }
 
 // static