classes/create-spdx: handle if IMAGE_LINK_NAME is empty

If IMAGE_LINK_NAME is set to "" (supported in other classes) then skip
creating symlinks for the spdx manifest files.

(From OE-Core rev: c2d5e2dbbba78d8d7036f6418360b2e84bcdc169)

Signed-off-by: Paul Eggleton <paul.eggleton@microsoft.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/create-spdx.bbclass

@@ -870,8 +870,9 @@ python image_combine_spdx() {
     with image_spdx_path.open("wb") as f:
         doc.to_json(f, sort_keys=True)
 
-    image_spdx_link = imgdeploydir / (image_link_name + ".spdx.json")
-    image_spdx_link.symlink_to(os.path.relpath(image_spdx_path, image_spdx_link.parent))
+    if image_link_name:
+        image_spdx_link = imgdeploydir / (image_link_name + ".spdx.json")
+        image_spdx_link.symlink_to(os.path.relpath(image_spdx_path, image_spdx_link.parent))
 
     num_threads = int(d.getVar("BB_NUMBER_THREADS"))
 
@@ -942,8 +943,9 @@ python image_combine_spdx() {
             tar.addfile(info, fileobj=index_str)
 
     def make_image_link(target_path, suffix):
-        link = imgdeploydir / (image_link_name + suffix)
-        link.symlink_to(os.path.relpath(target_path, link.parent))
+        if image_link_name:
+            link = imgdeploydir / (image_link_name + suffix)
+            link.symlink_to(os.path.relpath(target_path, link.parent))
 
     make_image_link(spdx_tar_path, ".spdx.tar.zst")