[gimp] app: (selection editor) fix clicking on selection mask or dropping color

[Jehan <jehanp src gnome org>]

commit bd452d7df1162e026eb3b0ba2ebe72c133ce96e2
Author: Jehan <jehan girinstud io>
Date:   Mon Aug 17 13:32:36 2020 +0200

    app: (selection editor) fix clicking on selection mask or dropping color
    
    I discover that the selection editor has these hidden features that (1)
    you can click on the selection mask (in the editor dockable) and it
    behaves like the Select by Color tool (not sure exactly how useful this
    feature is as you can't really see where you click though) and (2) you
    can drop a color and it will select this color also as though clicked by
    the Select by Color tool (which looks quite useful!).
    These features use the option values as set in the Select by Color tool.
    
    Unfortunately both these features were broken when a non-zero threshold
    was set because it expects a [0-1] range whereas threshold is [0-255].
    Fix the parameters in gimp_channel_select_by_color() call.

 app/widgets/gimpselectioneditor.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/app/widgets/gimpselectioneditor.c b/app/widgets/gimpselectioneditor.c
index 38b60f5fbc..69e6f95dab 100644
--- a/app/widgets/gimpselectioneditor.c
+++ b/app/widgets/gimpselectioneditor.c
@@ -286,7 +286,7 @@ gimp_selection_view_button_press (GtkWidget           *widget,
                                     drawable,
                                     options->sample_merged,
                                     &color,
-                                    options->threshold,
+                                    options->threshold / 255.0,
                                     options->select_transparent,
                                     options->select_criterion,
                                     operation,
@@ -334,7 +334,7 @@ gimp_selection_editor_drop_color (GtkWidget     *widget,
                                 drawable,
                                 options->sample_merged,
                                 color,
-                                options->threshold,
+                                options->threshold / 255.0,
                                 options->select_transparent,
                                 options->select_criterion,
                                 sel_options->operation,