devtool / lib/oe/recipeutils: ensure we can parse without bbappends

These functions ostensibly allowed parsing a recipe without bbappends
but this clearly hadn't been tested because a variable was unassigned in
both of them in that case.

(From OE-Core rev: d2bb9f08303bb120e811c03af2f5339e8f262cfa)

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

scripts/lib/devtool/__init__.py

@@ -134,6 +134,8 @@ def parse_recipe(config, tinfoil, pn, appends):
         # Filter out appends from the workspace
         append_files = [path for path in append_files if
                         not path.startswith(config.workspace_path)]
+    else:
+        append_files = None
     return oe.recipeutils.parse_recipe(recipefile, append_files,
                                        tinfoil.config_data)