[gthumb] Include locale.h for LC_NUMERIC

[Paolo Bacchilega <paobac src gnome org>]

commit d8c6afbfed31495d97726ffe88b020ebd30413c9
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Mon Jun 28 12:09:28 2021 +0200

    Include locale.h for LC_NUMERIC
    
    Fixes https://gitlab.gnome.org/GNOME/gthumb/-/issues/180

 extensions/file_tools/gth-file-tool-color-picker.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/extensions/file_tools/gth-file-tool-color-picker.c 
b/extensions/file_tools/gth-file-tool-color-picker.c
index 5259cae9..e323809e 100644
--- a/extensions/file_tools/gth-file-tool-color-picker.c
+++ b/extensions/file_tools/gth-file-tool-color-picker.c
@@ -21,6 +21,7 @@
 
 #include <config.h>
 #include <math.h>
+#include <locale.h>
 #include <gthumb.h>
 #include <extensions/image_viewer/gth-image-viewer-page.h>
 #include "gth-file-tool-color-picker.h"