Log lines longer than 16384 characters are improperly joined

[charliefoxtwo]

Bug description
Per moby/moby#22982 and moby/moby#32923, the max length of a line logged in docker is 16k. When the line gets longer, it is streamed to multiple line entries in the log file. This looks like so:

{"log":"<15k+ characters> ... this is a sin","stream":"stdout","time":"2019-12-05T00:26:59.526348635Z"}
{"log":"gle log entry.\n","stream":"stdout","time":"2019-12-05T00:26:59.526348635Z"}}

However, the point where these lines should join when viewing a container's logs in portainer appears to have some sort of special character (�). In my case, this renders as either <15k+ characters> ... this is a sin�gle log entry. or with an @ symbol instead (though this isn't actually the symbol - I have no idea what it actually is).

Expected behavior
The line should display as <15k+ characters> ... this is a single log entry.

Steps to reproduce the issue:

1. Create a container which will attempt to log a line larger than 16384 UTF-8 characters
2. View container logs in portainer web view
   a. If things render fine, attempt to copy text and notice there will be a weird character at the cutoff point
   b. Alternatively, open developer tools in browser and view source

Technical details:

• Portainer version: 1.22.2
• Docker version (managed by Portainer): 18.09.3
• Platform (windows/linux): linux
• Command used to start Portainer (docker run -p 9000:9000 portainer/portainer): probably that, but I'm unsure
• Browser: Firefox 71.0b10 (64-bit)

Additional context
When viewing the log file for the container via docker logs, the entries appear to be joined together with no errors.

[ghost]

Reproduced on 1.23.2

[ghost]

This will be addressed in #3749