Fix some minor bugs related to imports in the new mojom bindings generator.

mojo/public/tools/bindings/run_code_generators.py

Index: mojo/public/tools/bindings/run_code_generators.py
diff --git a/mojo/public/tools/bindings/run_code_generators.py b/mojo/public/tools/bindings/run_code_generators.py
index 6f278a350fcb560dbe3b2c2454ea47be8ee8560d..ebe2f1f69f3db2d551f1b8642ca308dc7e14b031 100755
--- a/mojo/public/tools/bindings/run_code_generators.py
+++ b/mojo/public/tools/bindings/run_code_generators.py
@@ -129,6 +129,8 @@ def FixModulePath(module, src_root_path):
     abs_root: {str} absolute path to the root of the source tree.
   """
   module.path = os.path.relpath(module.path, src_root_path)
+  if not hasattr(module, 'imports'):
+    return
   for import_dict in module.imports:
     FixModulePath(import_dict['module'], src_root_path)