[metacity] screen: fix build warnings

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 80c36da44f094d0c20aa67bb04125ba141083626
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Sun Sep 20 06:52:51 2015 +0300

    screen: fix build warnings

 src/core/screen.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)
---
diff --git a/src/core/screen.c b/src/core/screen.c
index c086cef..b0f1e29 100644
--- a/src/core/screen.c
+++ b/src/core/screen.c
@@ -2072,7 +2072,7 @@ meta_screen_queue_workarea_recalc (MetaScreen *screen)
 
 
 #ifdef WITH_VERBOSE_MODE
-static char *
+static const gchar *
 meta_screen_corner_to_string (MetaScreenCorner corner)
 {
   switch (corner)
@@ -2085,6 +2085,8 @@ meta_screen_corner_to_string (MetaScreenCorner corner)
       return "BottomLeft";
     case META_SCREEN_BOTTOMRIGHT:
       return "BottomRight";
+    default:
+      break;
     }
 
   return "Unknown";
@@ -2298,6 +2300,8 @@ meta_screen_calc_workspace_layout (MetaScreen          *screen,
             }
         }
       break;
+    default:
+      break;
     }
 
   if (i != grid_area)
@@ -2698,6 +2702,9 @@ meta_screen_sn_event (SnMonitorEvent *event,
                   "Received startup canceled for %s\n",
                   sn_startup_sequence_get_id (sequence));
       break;
+
+    default:
+      break;
     }
 }
 #endif