ui: gtk: fix crash when terminal inner-border is NULL

VTE terminal inner-border can be NULL. The vte-0.36 (API 2.90)
code checks for the condition too so I assume it's not just a bug

Fixes a crash on Fedora 24 with gtk 3.20
Signed-off-by: NCole Robinson <crobinso@redhat.com>
Message-id: 2b2e85d403e8760ea53afd735a170500d5c17716.1462557436.git.crobinso@redhat.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

ui/gtk.c

@@ -340,10 +340,12 @@ static void gd_update_geometry_hints(VirtualConsole *vc)
         geo.min_height = geo.height_inc * VC_TERM_Y_MIN;
         mask |= GDK_HINT_MIN_SIZE;
         gtk_widget_style_get(vc->vte.terminal, "inner-border", &ib, NULL);
-        geo.base_width  += ib->left + ib->right;
-        geo.base_height += ib->top + ib->bottom;
-        geo.min_width   += ib->left + ib->right;
-        geo.min_height  += ib->top + ib->bottom;
+        if (ib) {
+            geo.base_width  += ib->left + ib->right;
+            geo.base_height += ib->top + ib->bottom;
+            geo.min_width   += ib->left + ib->right;
+            geo.min_height  += ib->top + ib->bottom;
+        }
         geo_widget = vc->vte.terminal;
 #endif
     }