[BUG] wrong size split when volume set to 7.8g or 15.6g

[yanshenxian]

Configuration
Keka version: [1.1.28 (3465)]
macOS version: [10.15.3 (19D76)]

Describe the bug
I choose to set a volume for 7.8gb or 15.6gb, but it output 7800000b per volume

2020-05-18 01:27:44.515 Set tarball: 0. Tarball active: 0. Extension: zip
2020-05-18 01:27:44.517 Binary used: keka7z
2020-05-18 01:27:44.518 Arguments: (
    a,
    "-tzip",
    "-v7800000b",
    "-mx1",
    "-p12345",
    "/Users/yanshen.xian/Downloads/Video/The.World.of.the.Married.S01E01.1080p.WEB-DL.H264.AAC-AppleTor.mp4.zip",
    "/Users/yanshen.xian/Downloads/Video/The.World.of.the.Married.S01E01.1080p.WEB-DL.H264.AAC-AppleTor.mp4"
)
2020-05-18 01:27:44.555 Compression output: 

7-Zip [64] 16.02 : Copyright (c) 1999-2016 Igor Pavlov : 2016-05-21
p7zip Version 16.02 (locale=utf8,Utf16=on,HugeFiles=on,64 bits,8 CPUs x64)
Modified by aONe for Keka

Scanning the drive:
  0M Scan  /Users/yanshen.xian/Downloads/Video/
2020-05-18 01:27:44.556 Compression output: 
�����������������������������������������������                                               �����������������������������������������������1 file, 3817924199 bytes (3642 MiB)

Creating archive: /Users/yanshen.xian/Downloads/Video/The.World.of.the.Married.S01E01.1080p.WEB-DL.H264.AAC-AppleTor.mp4.zip

Items to compress: 1

Screenshots

Additional context
any other size like 700MB is ok. except 7.8g and 15.6g

[aonez]

Thanks for that one @yanshenxian! Fixing it right away.