Tighten checks when normalizing codepositions

Author: Gustavo2622

src/ecMatching.ml

@@ -311,7 +311,7 @@ module Position = struct
 
   (* Throws InvalidCPos if failing — allows [0, n] where n is "after last" *)
   let check_nm_cpos1 (nm: nm_codepos1) (s: stmt) : unit =
-    if nm < 0 || nm > List.length s.s_node then raise InvalidCPos
+    if nm < 0 || nm >= List.length s.s_node then raise InvalidCPos
 
   (* Normalizes code position wrt stmt — input is 0-indexed *)
   let normalize_cp_base ?(check = true) (env: EcEnv.env) (cb: cp_base) (s: stmt) : nm_codepos1 =