CC Mode: check for and fix missing call to before_change_functions.

CC Mode: check for and fix missing call to before_change_functions.

Fixes bug #24094 and bug #24074.

This can happen with `revert-buffer' or sometimes `find-file', when the file
is already in a buffer, but the file has been changed outside of Emacs.

* lisp/progmodes/cc-mode (c-after-change): When we detect a missing
invocation of c-before-change-functions, we assume the changed region is the
entire buffer, and call c-before-change explicitly before proceding.