[QScintilla] Possible bug with 'selectedText' while Ctrl+Mouse movement

[Matic Kukovec]

Hi,

This bug is only present on Linux!

In the attachment is an example of the error. How to reproduce it:
Without changing any text inside the QScintilla editor, set the cursor to the beginning of the first line, press and hold the CTRL key and drag the mouse to the end of the first line. After selecting a few characters, usually more than 5 or 6, the example throws a exception, something like:

*** Error in `/usr/bin/python3': free(): invalid next size (fast): 0x01e8d3e8 ***
Aborted

The error appears to happen when calling the selectedText method, while the CTRL key is pressed and changing the selected text with the mouse.
The returned string from selectedText is not correct, which is visible in the console window in the example just before the exception is thrown.

This error was found and reproduced in multiple editors, including: ExCo, mu-editor and meditor.
Probably every editor based on QScintilla has this issue.

Tested on:

  *   Lubuntu x64, PyQt 5.11.2, QScintilla 2.11.4
  *   Raspbian RaspberryPI 3 (arm), PyQt 5.7, QScintilla 2.9.3

Regards,
Matic
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