[gnome-software] trivial: Fix a -Wimplicit-fallthrough warning with gcc 7

[Kalev Lember <klember src gnome org>]

commit 1ada14bbe30c32ae9887f03376407824954da13c
Author: Kalev Lember <klember redhat com>
Date:   Sun Jan 29 14:46:31 2017 +0100

    trivial: Fix a -Wimplicit-fallthrough warning with gcc 7

 src/gs-shell-details.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/gs-shell-details.c b/src/gs-shell-details.c
index cd3358f..f0087f4 100644
--- a/src/gs-shell-details.c
+++ b/src/gs-shell-details.c
@@ -435,6 +435,7 @@ gs_shell_details_refresh_progress (GsShellDetails *self)
                        gtk_widget_set_visible (self->progressbar_top, TRUE);
                        break;
                }
+               /* FALLTHROUGH */
        default:
                gtk_widget_set_visible (self->label_progress_percentage, FALSE);
                gtk_widget_set_visible (self->progressbar_top, FALSE);