[gthumb] webp can have transparency as well

[Paolo Bacchilega <paobac src gnome org>]

commit 5298d2cf833dd5300b1c3b17106fe256f3834c83
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Sun Jan 10 18:03:18 2021 +0100

    webp can have transparency as well

 gthumb/glib-utils.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/gthumb/glib-utils.c b/gthumb/glib-utils.c
index 31b91091..d7cb4c49 100644
--- a/gthumb/glib-utils.c
+++ b/gthumb/glib-utils.c
@@ -1909,7 +1909,8 @@ _g_mime_type_has_transparency (const char *mime_type)
 
        return (strcmp (mime_type, "image/png") == 0)
                || (strcmp (mime_type, "image/gif") == 0)
-               || (strcmp (mime_type, "image/svg+xml") == 0);
+               || (strcmp (mime_type, "image/svg+xml") == 0)
+               || (strcmp (mime_type, "image/webp") == 0);
 }