[gedit] Fixes backscape not working as clean up key in the external tool pluggin

[Jordi Mas <jmas src gnome org>]

commit 5fa0bffb922497d2cc1e8fe579f0f0c05bc0b4c1
Author: Jordi Mas <jmas softcatala org>
Date:   Wed Apr 17 18:18:21 2019 +0200

    Fixes backscape not working as clean up key in the external tool pluggin

 plugins/externaltools/tools/manager.py | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/plugins/externaltools/tools/manager.py b/plugins/externaltools/tools/manager.py
index b29191beb..07f58c3e9 100644
--- a/plugins/externaltools/tools/manager.py
+++ b/plugins/externaltools/tools/manager.py
@@ -701,6 +701,8 @@ class Manager(GObject.Object):
             self.update_accelerator_label()
             self['commands'].grab_focus()
             return True
+        elif event.keyval == Gdk.KEY_BackSpace:
+            return False
         elif event.keyval in range(Gdk.KEY_F1, Gdk.KEY_F12 + 1):
             # New accelerator
             if self.set_accelerator(event.keyval, mask):