[pan2] Fix error found by valgrind: 600 bytes in 100 blocks are definitely lost in loss record 10, 929 of 11

[Petr Kovář <pmkovar src gnome org>]

commit dfd5c32d7ea51c2aac3599cf76ed3a8c83ee38d5
Author: Olaf Seibert <rhialto falu nl>
Date:   Fri Mar 18 01:31:34 2016 +0100

    Fix error found by valgrind: 600 bytes in 100 blocks are definitely lost in loss record 10,929 of 11,334
    
       at 0x4C2BBCF: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
       by 0x6D2F578: g_malloc (in /lib/x86_64-linux-gnu/libglib-2.0.so.0.4600.2)
       by 0x6D4832E: g_strdup (in /lib/x86_64-linux-gnu/libglib-2.0.so.0.4600.2)
       by 0x6AC70AC: ??? (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.4600.2)
       by 0x524D9EF: gtk_tree_model_get_valist (in /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0.2400.28)
       by 0x524DC98: gtk_tree_model_get (in /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0.2400.28)
       by 0x4906F2: pan::HeaderPane::render_date(_GtkTreeViewColumn*, _GtkCellRenderer*, _GtkTreeModel*, 
_GtkTreeIter*, void*) (header-pane.cc:335)
       by 0x527C399: gtk_tree_view_column_cell_set_cell_data (in 
/usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0.2400.28)
    ...
       by 0x4766A4: mainloop (pan.cc:95)
       by 0x4766A4: run_pan_in_window (pan.cc:554)
       by 0x4766A4: main (pan.cc:1110)
    
    lost 6 bytes every time a date is displayed.

 pan/gui/header-pane.cc |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/pan/gui/header-pane.cc b/pan/gui/header-pane.cc
index c63177b..94417e4 100644
--- a/pan/gui/header-pane.cc
+++ b/pan/gui/header-pane.cc
@@ -338,6 +338,7 @@ HeaderPane :: render_date  (GtkTreeViewColumn * ,
                 "background", self->_bg.c_str(),
                 "foreground", self->_fg.c_str(),
                 NULL);
+  g_free (date);
 }
 
 struct HeaderPane::CountUnread: public PanTreeStore::WalkFunctor