Hello,

`python-shell-send-region' fails with the following error when the
region starts in the middle of the first line.

Wrong type argument: wholenump, -1

This is caused by the code to insert the coding cookie in
`python-shell-buffer-substring'.  I think that the current code
assumes that the region begins at line beginning position.  However,
there are some use-cases where the region starts in the middle of the
line as discussed in #60142.  So I think the special treatment in case
of point-min should be extended to case of first line.  Attached is a
patch to implement this.

--

In GNU Emacs 30.0.50 (build 6, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.16.0, Xaw scroll bars) of 2023-01-01 built on ubuntu
Repository revision: 9596e683834a36060497903b47b870b338d88095
Repository branch: master
System Description: Ubuntu 22.04.1 LTS

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