1 line non-UTF8 file gets garbled

Summary

Non-utf8 characters are garbled if file only contains 1 line.

Environment

• v4.14.4
  • Verified in Bitbucket Server AMI

Steps to Reproduce

• Activate diff transcoding
  1. Commit and push 1 line non-utf8 file
  2. Check the added file gets corrupt
• Deactivate diff transcoding
  1. Commit and push 1 line non-utf8 file
  2. Check the added file gets corrupt

I've attached the file non_utf8.zip which is used for verification.

$ find . -type f -name "*.txt" | xargs nkf --guess
./1.1.txt: Shift_JIS (LF)
./1.txt: Shift_JIS (LF)
./2.1.txt: EUC-JP (LF)
./2.txt: EUC-JP (LF)
./3.1.txt: EUC-JP (LF)
./3.txt: EUC-JP (LF)

Expected Results

Source view correctly shows 1 line file as well as multi lines file.

Actual Results

-	1 line file	Multi lines file
Transcode-enabled	Source view Diff to previous	Source view Diff to previous
Transcode-disabled	Source view Diff to previous	Source view Diff to previous

• Legend:
  • Fine
  • Corrupt
  • Expectedly corrupt cf. https://jira.atlassian.com/browse/BSERV-3179
• Tested encodings
  • Shit_JIS
  • EUC-JP

Workaround

• None