gtk: fix uninitialized variable

zoom_to_fit is never initialized to false, Coverity complains
(not sure why GCC does not).

Fixes: e8b1386e
Cc: kraxel@redhat.com
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20181003121138.22037-1-pbonzini@redhat.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

ui/gtk.c

@@ -2138,7 +2138,7 @@ static GSList *gd_vc_gfx_init(GtkDisplayState *s, VirtualConsole *vc,
                               QemuConsole *con, int idx,
                               GSList *group, GtkWidget *view_menu)
 {
-    bool zoom_to_fit;
+    bool zoom_to_fit = false;
 
     vc->label = qemu_console_get_label(con);
     vc->s = s;