fru_gen: Handle empty yaml files

Allow the build to work in the event of an empty
YAML file.

Change-Id: I3d36b57852446959aeb836ab69958c16387c02fc
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/scripts/fru_gen.py b/scripts/fru_gen.py
index 391bb5f..aca86e8 100755
--- a/scripts/fru_gen.py
+++ b/scripts/fru_gen.py
@@ -10,6 +10,8 @@
 def generate_hpp(inventory_yaml, output_dir):
     with open(os.path.join(script_dir, inventory_yaml), 'r') as f:
         ifile = yaml.safe_load(f)
+        if not isinstance(ifile, dict):
+            ifile = {}
 
         # Render the mako template