Upload should work without internet connectivity

### How to use GitHub

* Please use the 👍 [reaction](https://blog.github.com/2016-03-10-add-reactions-to-pull-requests-issues-and-comments/) to show that you are interested into the same feature.
* Please don't comment if you have no relevant information to add. It's just extra noise for everyone subscribed to this issue.
* Subscribe to receive notifications on status change and new comments.

**Is your feature request related to a problem? Please describe.**
When connected to a WiFi access point with no internet connectivity, uploads do not work, even if connectivity to Nextcloud is fine.

I stumbled across this when our internet connection went down for a day. I could access my Nextcloud instance via the Android app and download files etc. fine because it's all on my internal network and my phone was still connected to WiFi. However, uploads did not work.

**Describe the solution you'd like**
I assume this is happening because the app is checking for internet connectivity before uploading (saw a vague comment aluding to this from a few years ago), whereas what it really should be doing is checking it can connect to the Nextcloud server in question.

**Describe alternatives you've considered**
I don't see any reason why uploads shouldn't work when connectivity to the Nextcloud server is working fine.

**Additional context**
N/A