Check result from c-backward-token-2 to avoid infinite loop

This fixes bug #33784.

* lisp/progmodes/cc-fonts.el (c-get-fontification-context): While moving back
over enclosing parentheses, check that c-backward-token-2 actually moves.

lisp/progmodes/cc-fonts.el

@@ -1284,7 +1284,7 @@ casts and declarations are fontified.  Used on level 2 and higher."
 		(save-excursion
 		  (goto-char match-pos)
 		  (while
-		      (progn (c-backward-token-2)
+		      (and (zerop (c-backward-token-2))
 			   (eq (char-after) ?\()))
 		  (looking-at c-arithmetic-op-regexp)))
 	   (cons nil nil))