Fix list duplication error in define_image_type.

* image.c (define_image_type): Avoid adding duplicate types to
image_types.  Suggested by Jörg Walter.

Fixes: debbugs:12463

1 files changed, 7 insertions, 1 deletions

diff --git a/src/image.c b/src/image.c
index 8fc1c8637eb..8d690df8abb 100644
--- a/src/image.c
+++ b/src/image.c
@@ -590,9 +590,15 @@ define_image_type (struct image_type *type, int loaded)
     success = Qnil;
   else
     {
+      struct image_type *p;
+      Lisp_Object target_type = *(type->type);
+      for (p = image_types; p; p = p->next)
+        if (EQ (*(p->type), target_type))
+          return Qt;
+
       /* Make a copy of TYPE to avoid a bus error in a dumped Emacs.
          The initialized data segment is read-only.  */
-      struct image_type *p = xmalloc (sizeof *p);
+      p = xmalloc (sizeof *p);
       *p = *type;
       p->next = image_types;
       image_types = p;