[PATCH] prevent null-pointer dereference

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Hi,

I found a NULL-pointer dereference at jbig2_image_clone in
jbig2_image.c:61 with current git version (c29b63557cb191f)

It occurs if jbig2dec is called with <global_stream> <page_stream> and
no page segment with image description is inside <page_stream>.
Function jbig2_page_out tries to jbig2_image_clone with a null-pointer.

The attached patch should fix this. Please merge it.

Regards,
Georg

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diff --git a/jbig2_image.c b/jbig2_image.c
index 7037d71..45db3b3 100644
--- a/jbig2_image.c
+++ b/jbig2_image.c
@@ -60,7 +60,9 @@ Jbig2Image* jbig2_image_new(Jbig2Ctx *ctx, int width, int height)
 /* clone an image pointer by bumping its reference count */
 Jbig2Image* jbig2_image_clone(Jbig2Ctx *ctx, Jbig2Image *image)
 {
-	image->refcount++;
+	if (image != NULL)
+		image->refcount++;
+
 	return image;
 }

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