dist.ndk_api: actually default to None, instead of 0

Author: tshirtman

pythonforandroid/distribution.py

@@ -193,7 +193,7 @@ def get_distributions(cls, ctx, extra_dist_dirs=[]):
                 if 'ndk_api' in dist_info:
                     dist.ndk_api = dist_info['ndk_api']
                 else:
-                    dist.ndk_api = 0
+                    dist.ndk_api = None
                     warning(
                         "Distribution {distname}: (distdir) has been "
                         "built with an unknown api target, ignoring it, "