[gtk+] Avoid compiler warnings

[Matthias Clasen <matthiasc src gnome org>]

commit 29e8a07ddd123cbf91207f7a0e2c38a016d1f3d7
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Jul 19 20:45:52 2017 -0400

    Avoid compiler warnings
    
    Initialize these variables, so gcc doesn't complain.

 gtk/gtkcenterbox.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtkcenterbox.c b/gtk/gtkcenterbox.c
index 8b89df5..2e15f04 100644
--- a/gtk/gtkcenterbox.c
+++ b/gtk/gtkcenterbox.c
@@ -329,8 +329,8 @@ gtk_center_box_measure_opposite (GtkWidget      *widget,
 
   if (above_min >= 0)
     {
-      int min_baseline;
-      int nat_baseline;
+      int min_baseline = -1;
+      int nat_baseline = -1;
 
       total_min = MAX (total_min, above_min + below_min);
       total_nat = MAX (total_nat, above_nat + below_nat);