[BUG] face problem with git install package

I got a package installed by this
```
pip3 install git+https://github.com/floxay/python-riot-auth.git
```
if i use `pip3 freeze > requirements.txt`,the result be like(this is the right one)
```
riot-auth @ git+https://github.com/floxay/python-riot-auth.git@e70f76002728b99005baccd6fe3157c03d4d9f02
```
but use `pipreqs . --encoding=utf8 --force`,the result is wrong
```
requests==2.28.1
riot_auth==1.0.3
zhconv==1.4.3
```
riot_auth is not in pypl, can't install by `pip3 install riot_auth`
```
ERROR: Could not find a version that satisfies the requirement riot_auth==1.0.3 (from versions: none)
ERROR: No matching distribution found for riot_auth==1.0.3
```

Reproduce the discrepancy with pipreqs using the pip3-installed Git package and compare its output with pip freeze. Start by tracing how pipreqs resolves imported package names and writes requirements.txt; done means the generated requirement preserves an installable Git reference rather than the unavailable riot_auth==1.0.3 entry.

Written by the indexing model from the issue text.