[matcher] show proper error on case without pattern

src/typing/matcher.ml

@@ -550,7 +550,7 @@ module Case = struct
 				let e2 = collapse_case el in
 				EBinop(OpOr,e,e2),punion (pos e) (pos e2)
 			| [] ->
-				die "" __LOC__
+				error "case without pattern" p
 		in
 		let e = collapse_case el in
 		let monos = List.map (fun _ -> mk_mono()) ctx.type_params in