GTK: fix compilation with GCC 7

Change-Id: Ifde706f4705af406fd4eee61a312d8eb0976d972
Reviewed-on: https://code.wireshark.org/review/22598
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>

ui/gtk/gui_utils.c

@@ -1281,7 +1281,7 @@ tree_view_key_pressed_cb(GtkWidget   *tree,
                 rc = TRUE;
                 break;
             }
-            /* No break - fall through to jumping to the parent */
+            /* else fall through to jumping to the parent */
         case GDK_BackSpace:
             if (!expanded) {
                 /* subtree is already collapsed, jump to parent node */

ui/gtk/rlc_lte_graph.c

@@ -2190,7 +2190,7 @@ static gboolean key_press_event(GtkWidget *widget _U_, GdkEventKey *event, gpoin
             do_zoom_out_keyboard(g,
                                  FALSE,
                                  event->state & GDK_CONTROL_MASK);
-
+            break;
         /* Direction keys */
         case GDK_Left:
             do_key_motion_left(g, step);