Specifying -p on command line can lead to data corruption

[sasumner]

Description of the Issue

Similar to the data corruption that can happen with the Goto dialog's Offset option (see #9101 and #9129 (comment) ) , the -p command line parameter can set the current position between the bytes of a multibyte-encoded UTF-8 character, or between the bytes of a Windows' line-ending of a CRLF pair. This should not be allowed to occur.

Multibyte UTF-8 characters should be be considered "atomic" (strong feeling about) and so should Windows' line-endings (less strong of a feeling, but still fairly strong).

Steps to Reproduce the Issue

1. Turn visible line-endings on via View menu > Show symbol > Show End of Line
2. Open test_4byte_utf8.txt file (attached, below), observe the UTF-8 character (after zooming):
   
3. Optional, using HexEditor plugin, look at hex view, observe:
   
4. Open test_crlf.txt file (attached, below), observe:
   
5. Close all files; quit Notepad++
6. Run the command line: notepad++.exe -p1 test_4byte_utf8.txt using the attached file of the same name
7. After the file loads but before doing anything else, type a
8. Observe data is corrupted as the 4-byte UTF-8 character has been split:
   
9. Repeat steps 5 through 7 using the test_crlf.txt file instead of the test_4byte_utf8.txt file in step 6.
10. Observe line-endings, which should be CRLF, are "corrupted"; one line-ending is CR, the other is LF:
    

Expected Behavior

No data corruption.

Actual Behavior

The data corruption shown in steps 8 and 10.

Debug Information

Notepad++ v7.9.1 (64-bit)
Build time : Nov 2 2020 - 01:07:46
Path : C:\........\npp.7.9.1.portable.x64\notepad++.exe
Admin mode : OFF
Local Conf mode : ON
OS Name : Windows 10 Enterprise (64-bit)
OS Version : 1809
OS Build : 17763.1518
Current ANSI codepage : 1252
Plugins : mimeTools.dll NppConverter.dll NppExport.dll

Test files

test_4byte_utf8.txt
test_crlf.txt

[sasumner]

Probably also want to tick the box for Use DirectWrite... in the Preferences