[gimp/gtk3-port] imagemap: fix invalid source removal

[Simon Budig <simon src gnome org>]

commit ccf5a5daf0061b453d1c6ba179f24b60c80d2a0f
Author: Simon Budig <simon budig de>
Date:   Sat May 5 20:00:19 2018 +0200

    imagemap: fix invalid source removal

 plug-ins/imagemap/imap_main.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/plug-ins/imagemap/imap_main.c b/plug-ins/imagemap/imap_main.c
index 446cbac..d0caa49 100644
--- a/plug-ins/imagemap/imap_main.c
+++ b/plug-ins/imagemap/imap_main.c
@@ -1024,6 +1024,8 @@ key_timeout_cb(gpointer data)
       break;
    }
    preview_redraw();
+
+   _timeout = 0;
    return FALSE;
 }