Global config cannot be set if ~/.gitconfig does not exist yet

When there is no ~/.gitconfig, the following code snippet

import pygit2
global_config = pygit2.Config.get_global_config() # ← Exception raised here
global_config['user.email'] = 'me@example.org'

fails with

Traceback (most recent call last):
  File "global_config.py", line 2, in <module>
    global_config = pygit2.Config.get_global_config()
  File "/usr/lib/python3/dist-packages/pygit2/config.py", line 281, in get_global_config
    return Config._from_found_config(C.git_config_find_global)
  File "/usr/lib/python3/dist-packages/pygit2/config.py", line 265, in _from_found_config
    check_error(err, True)
  File "/usr/lib/python3/dist-packages/pygit2/errors.py", line 53, in check_error
    raise IOError(message)
OSError: the global file '.gitconfig' doesn't exist: No such file or directory

I.e.,

1. there seems to be no way of setting a global option unless ~/.gitconfig already exists.
2. There seems to be no way to create the global config file ahead of time, at least not in a portable way (I doubt it is in ~/.gitconfig on Windows systems).

首先，在没有 ~/.gitconfig 的情况下重现提供的 Python 代码片段，然后检查 pygit2/config.py，尤其是 Config.get_global_config 和 _from_found_config。当无需已有的全局配置文件即可设置全局选项，并且在其位置不同的平台上也能做到这一点时，修复就完成了。