[gthumb] make sure the has_alpha flag is a boolean value

[Paolo Bacchilega <paobac src gnome org>]

commit 3321208acb105e881e2ca5bd70006e40005d45b2
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Sat Apr 20 17:09:33 2019 +0200

    make sure the has_alpha flag is a boolean value

 gthumb/cairo-utils.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gthumb/cairo-utils.c b/gthumb/cairo-utils.c
index 9b20e682..babed8b8 100644
--- a/gthumb/cairo-utils.c
+++ b/gthumb/cairo-utils.c
@@ -104,7 +104,7 @@ _cairo_metadata_set_has_alpha (cairo_surface_metadata_t     *metadata,
                               gboolean                  has_alpha)
 {
        metadata->valid_data |= _CAIRO_METADATA_FLAG_HAS_ALPHA;
-       metadata->has_alpha = has_alpha;
+       metadata->has_alpha = has_alpha ? TRUE : FALSE;
 }