Fix Windows build after PR 75 about ros-galactic HOT 10 CLOSED

mamba create -n testenv python=3.9 pip rospkg networkx "catkin_pkg>=0.4.16" "ruamel.yaml>=0.16.6" "rosdistro>=0.8.0" "empy>=3.3.4" boa=0.9
mamba activate testenv
pip install git+https://github.com/RoboStack/vinca.git --no-deps
cd /path/to/ros-galactic
copy vinca_win.yaml vinca.yaml
vinca --platform win-64
boa build additional_recipes/ros2-distro-mutex/ -m ./.ci_support/conda_forge_pinnings.yaml -m ./conda_build_config.yaml
boa build . -m ./.ci_support/conda_forge_pinnings.yaml -m ./conda_build_config.yaml

Installing collected packages: wcwidth, json5, commonmark, sniffio, pygments, prompt-toolkit, joblib, rich, anyio, watchgod, boa
Successfully installed anyio-3.5.0 boa-0.10.0 commonmark-0.9.1 joblib-1.1.0 json5-0.9.6 prompt-toolkit-3.0.28 pygments-2.11.2 rich-12.0.1 sniffio-1.2.0 watchgod-0.8.1 wcwidth-0.2.5
"BUILDING RECIPE ros2-distro-mutex"

|   299             o.finalize_solve(sorted_outputs)                          |
|   300                                                                       |
|   301             meta = MetaData(recipe_path, o)                           |
| > 302             o.set_final_build_id(meta)                                |
|   303                                                                       |
|   304             if o.skip() or full_render:                               |
|   305                 continue                                              |
| C:\Miniconda\lib\site-packages\boa\core\recipe_output.py:576 in             |
| set_final_build_id                                                          |
|                                                                             |
|   573                     # remove self-run-exports for static packages     |
|   574                     run_exports_list[:] = []                          |
|   575                 else:                                                 |
| > 576                     x.eval_pin_subpackage([self])                     |
|   577                                                                       |
|   578                 x.eval_pin_subpackage([self])                         |
|   579             run_exports_list[:] = [x.final for x in run_exports_list] |
|                                                                             |
| C:\Miniconda\lib\site-packages\boa\core\conda_build_spec.py:161 in          |
| eval_pin_subpackage                                                         |
|                                                                             |
|   158             self.final = f"{pkg_name} {version} {build_string}"       |
|   159         else:                                                         |
|   160             version_parts = version.split(".")                        |
| > 161             count_pin = self.pin.max_pin.count(".")                   |
|   162             version_pin = ".".join(version_parts[: count_pin + 1])    |
|   163             version_pin += ".*"                                       |
|   164             self.final = f"{pkg_name} {version_pin}"                  |
+-----------------------------------------------------------------------------+
AttributeError: 'NoneType' object has no attribute 'max_pin'
##[error]Cmd.exe exited with code '1'.