[BUG] Wrong file length in the statusbar

Description of the Issue

After selecting proper 1-byte codepage in the menu the internal representation of data becomes unicoded. So the displayed length now is x2 times greater than it is.

It also breaks the HEX plugin, now it displays bullshit instead of raw file data.

Related: #16468 #15919

Steps To Reproduce

1. Open 1-byte txt

2. Select another 1-byte codepage.

3. See wrong length - now it's unicoded internally

Current Behavior

Length doubled

Expected Behavior

Correct length

Debug Information

Notepad++ v8.8.1   (64-bit)
Build time : May  3 2025 - 18:41:09
Scintilla/Lexilla included : 5.5.6/5.4.4
Boost Regex included : 1_85
Path : C:\Program Files\Notepad++\notepad++.exe
Command Line : "C:\Program Files\Notepad++\change.log" 
Admin mode : OFF
Local Conf mode : OFF
Cloud Config : OFF
Periodic Backup : OFF
Placeholders : OFF
Scintilla Rendering Mode : SC_TECHNOLOGY_DIRECTWRITE (1)
Multi-instance Mode : monoInst
File Status Auto-Detection : cdEnabledNew (for current file/tab only)
Dark Mode : OFF
OS Name : Windows 7 Professional (64-bit)
OS Build : 7601.0
Current ANSI codepage : 1251
Plugins : 
    BigFiles (0.1.3)
    ComparePlugin (2.0.2)
    helloworld (1)
    HexEditor (0.9.12)
    JSMinNPP (1.2205)
    MarkdownViewerPlusPlus (0.8.2)
    mimeTools (3.1)
    NppConverter (4.6)
    nppcrypt (1.0.1.6)
    NppExport (0.4)
    NppFTP (0.29.9)
    NppQrCode64 (0.0.0.1)
    ShtirlitzNppPlugin (1.1.2)
    XMLTools (3.1.1.13)

Anything else?

No response

No source files or tests are named. Reproduce the problem in Notepad++ v8.8.1 by opening a 1-byte text file and selecting another 1-byte codepage, then trace the statusbar length and HEX plugin data handling. Done means the displayed length remains correct and raw file data is preserved after the codepage change.