bug#38049: C mode fontification broken with reposition-window

[Juri Linkov]

Version: 27.0.50

This is a reproducible test case:

0. emacs -Q
1. C-x C-f emacs/lib-src/emacsclient.c
2. M-: (progn (search-forward "create-frame" nil t) (reposition-window))

Then half screen displays unfontified lines.

Fontification doesn't fail in other modes, only in C mode.

This has something to do with interaction between c-font-lock
and buffer navigation in reposition-window.