Windows-1251 text files unreadable in iOS OwnCloud Client

[Jupirage]

Client OwnCloud v3.6.2 iOS v11.0.3
Text files (*.txt) in Cyrillic (Windows 1251 encoding) are displayed with question marks instead of letters.

Steps to reproduce

1. At a Windows machine, open the notepad and type in some text in Cyrillic (Russian or Ukraine language for example).
2. Save the file in a folder mapped to OwnCloud repository. Give the file a name in Latin or Cyrillic (both are ok) and ".txt" extension.
3. Wait till the file is synchronized.
4. At an iPhone, open OwnCloud v3.6.2 Client application and browse to the folder mapped to the same repository.
5. Find and open the txt file previously saved.

Expected behavior

You expect to read your text in Russian or Ukraine.

Actual behaviour

All letters are substituted with black rectangles with question marks inside.

Server configuration

Unix Ubuntu 16

[michaelstingl]

related: #368