Fix erroneous upload handling

[Pittiplatsch]

Second try, now with unit test, and target "develop": Fix #21.

[samsonasik]

Could you rebase so only your commits shows in this PR, you can do with the following steps:

1. Ensure the upstream/origin set

git remote add upstream https://github.com/zendframework/zend-psr7bridge.git
git remote add origin https://github.com/Pittiplatsch/zend-psr7bridge 

2. Process rebase

git checkout develop && git pull upstream develop
git checkout fix_erroneous_upload_handling && git rebase develop
git push --force origin fix_erroneous_upload_handling

[Pittiplatsch]

Done.
Thx for detailed instructions 👍

[ezimuel]

@Pittiplatsch thanks for your contribution!

[Pittiplatsch]

You're welcome :-)