[glom] Check for empty() instead of size().

[Murray Cumming <murrayc src gnome org>]

commit 449086283c52bf3d52658a45156c549914f46524
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Oct 30 14:43:26 2015 +0100

    Check for empty() instead of size().
    
    Found by cppcheck.

 .../window_relationships_overview.cc               |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/glom/mode_design/relationships_overview/window_relationships_overview.cc 
b/glom/mode_design/relationships_overview/window_relationships_overview.cc
index fdeb7a3..a421fc9 100644
--- a/glom/mode_design/relationships_overview/window_relationships_overview.cc
+++ b/glom/mode_design/relationships_overview/window_relationships_overview.cc
@@ -142,7 +142,7 @@ void Window_RelationshipsOverview::draw_tables()
 {
   //Disconnect signal handlers for all current items,
   //so sigc::bind()ed RefPtrs can be released.
-  while(m_list_table_connections.size())
+  while(!m_list_table_connections.empty())
   {
      auto iter = m_list_table_connections.begin();
      sigc::connection the_connection = *iter;