build,json: fix build failure in case no data is found

Only collect arch_packages if actually generating any output.

Fixes: commit f09b9319 ("build,json: store arch_packages in profiles.json"(
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Paul Spooren <mail@aparcar.org>

scripts/json_overview_image_info.py

@@ -32,8 +32,8 @@ for json_file in work_dir.glob("*.json"):
                 image_info["profiles"][device_id]["images"][0]
             )
 
-
-default_packages, output["arch_packages"] = run(
+if output:
+    default_packages, output["arch_packages"] = run(
         [
             "make",
             "--no-print-directory",
@@ -46,11 +46,9 @@ default_packages, output["arch_packages"] = run(
         check=True,
         env=environ.copy().update({"TOPDIR": Path().cwd()}),
         text=True,
-).stdout.splitlines()
+    ).stdout.splitlines()
 
-output["default_packages"] = default_packages.split()
-
-if output:
+    output["default_packages"] = default_packages.split()
     output_path.write_text(json.dumps(output, sort_keys=True, separators=(",", ":")))
 else:
     print("JSON info file script could not find any JSON files for target")