Check if submodule exists before referencing

[tanaga9]

If you don't set the recursive option when you git clone
The following error:

Exception in thread Thread-1: Traceback (most recent call last): File "/usr/local/lib/python3.7/site-packages/git/objects/submodule/base.py", line 1037, in module repo = git.Repo(module_checkout_abspath) File "/usr/local/lib/python3.7/site-packages/git/repo/base.py", line 184, in __init__ raise InvalidGitRepositoryError(epath) git.exc.InvalidGitRepositoryError: /Users/tanaga/Inci_e3b_modules/Agents_e3b During handling of the above exception, another exception occurred: Traceback (most recent call last): File "/usr/local/lib/python3.7/site-packages/git/cmd.py", line 92, in pump_stream handler(line) File "/usr/local/lib/python3.7/site-packages/git/diff.py", line 534, in handle_diff_line '', change_type, score) File "/usr/local/lib/python3.7/site-packages/git/diff.py", line 286, in __init__ repo = submodule.module() File "/usr/local/lib/python3.7/site-packages/git/util.py", line 72, in wrapper return func(self, *args, **kwargs) File "/usr/local/lib/python3.7/site-packages/git/objects/submodule/base.py", line 1042, in module raise InvalidGitRepositoryError("No valid repository at %s" % module_checkout_abspath) git.exc.InvalidGitRepositoryError: No valid repository at /Users/tanaga/Inci_e3b_modules/Agents_e3b During handling of the above exception, another exception occurred: Traceback (most recent call last): File "/usr/local/Cellar/python/3.7.2_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/threading.py", line 917, in _bootstrap_inner self.run() File "/usr/local/Cellar/python/3.7.2_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/threading.py", line 865, in run self._target(*self._args, **self._kwargs) File "/usr/local/lib/python3.7/site-packages/git/cmd.py", line 95, in pump_stream raise CommandError(['<%s-pump>' % name] + cmdline, ex) git.exc.CommandError: Cmd('<stdout-pump>') failed due to: InvalidGitRepositoryError('No valid repository at /Users/tanaga/Inci_e3b_modules/Agents_e3b') cmdline: <stdout-pump> git diff-tree 1503302cd7ddc45641c8b03255e4c6cb6cebbcbe f900136f66bcbc675b24fd44a26c1a06520c7ed1 -r --abbrev=40 --full-index -M --raw --no-color 

This is useful for ci

[Byron]

Thanks a lot for the fix, your contribution is much appreciated :)!