Don't trigger save when gtk save dialog is closed by escape.

anntzer · anntzer · commit bc5add63001d · 2020-04-30T00:40:22.000+02:00
Pressing escape to close the gtk save dialog sets the return value
of `dialog.run()` to `ResponseType.DELETE_EVENT` rather than
`ResponseType.CANCEL` (and thus previously incorrectly triggered a
save), whereas checking for `ResponseType.OK` covers all cases.
diff --git a/lib/matplotlib/backends/backend_gtk3.py b/lib/matplotlib/backends/backend_gtk3.py
@@ -570,7 +570,7 @@ def on_notify_filter(*args):
         ff = dialog.get_filter()  # Doesn't autoadjust to filename :/
         fmt = self.canvas.get_supported_filetypes_grouped()[ff.get_name()][0]
         dialog.destroy()
-        if response == Gtk.ResponseType.CANCEL:
+        if response != Gtk.ResponseType.OK:
             return
         # Save dir for next time, unless empty str (which means use cwd).
         if mpl.rcParams['savefig.directory']:
