bug#45375: cc-mode indentation sometimes doesn't work

[Herman@debbugs.gnu.org, Géza <geza.herman@gmail.com>]

On current master (6af31fd71ff1a403c199c479577bcc145a547db1) indentation 
of C/C++ files sometimes doesn't work. I've bisected it: commit 
"9022df7027 Optimise c-parse-state for large buffers with few (if any) 
braces." introduced this behavior.

This is how to reproduce: check out 
9022df70270243f211c54ccd66800320148b8434, and execute "emacs -Q 
xdisp.c". Jump to line 2989 with M-g M-g 2989, move the cursor to the 
end of line of "Lisp_Object retval;", and press enter. The cursor will 
be moved to the correct place (correctly indented, cursor will be placed 
below the 'L' character of the previous line). Then push enter at end of 
line of "va_list ap;". For me, cursor will jump to the beginning of the 
line, it won't be indented. If I keep pressing enters, the next failure 
will be at "va_end (ap);". I'm not sure whether this exact steps 
reproduces for everyone, but it happened me 5 of 5 trials. If I don't 
press enter at the first line ("Lisp_Object retval;"), the problem 
doesn't happen for any of this function lines. But it will happen for 
somewhere else, if I keep trying (move around the file, press enter at 
random places: if will fail sooner or later).

For my configuration (without -Q), this problem happens quite frequently 
during editing C++ code.