bug#63272: 29.0.90; xref fails on long lines

[Juri Linkov <juri@linkov.net>]

1. Create a file with a long line, e.g. type

   a C-u 500000 b c

Save the file and commit to git.
(long-line-optimizations-p returns t)

2. Try to search a regexp that matches the whole long line, e.g.

   C-x p g a.*c RET

Debugger entered--Lisp error: (error "Stack overflow in regexp matcher")
  xref--collect-matches-1("a.*c" "/tmp/file" 1 1 500003 nil)
  xref--collect-matches((1 "/tmp/file" "abbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb...") "a.*c" #<buffer  *xref-temp*> nil)
  #f(compiled-function (hit) #<bytecode 0x122b1e80d7055e69>)((1 "/tmp/file" "abbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb..."))
  xref--convert-hits(((1 "/tmp/file" "abbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb...")) "a.*c")
  xref-matches-in-files("a.*c" ("/tmp/file"))
  project--find-regexp-in-files("a.*c" ("/tmp/file"))
  apply(project--find-regexp-in-files ("a.*c" ("/tmp/file")))
  #f(compiled-function (&rest args2) #<bytecode -0xae28f07f9498cbf>)()
  xref--show-xref-buffer(#f(compiled-function (&rest args2) #<bytecode -0xae28f07f9498cbf>) ((window . #<window 3 on tmp>) (display-action) (auto-jump)))
  xref--show-xrefs(#f(compiled-function (&rest args2) #<bytecode -0xae28f07f9498cbf>) nil)
  xref-show-xrefs(#f(compiled-function (&rest args2) #<bytecode -0xae28f07f9498cbf>) nil)
  project-find-regexp("a.*c")
  funcall-interactively(project-find-regexp "a.*c")
  call-interactively(project-find-regexp nil nil)
  command-execute(project-find-regexp)