Fix leak in BigInt unary plus (saghul)

Author: Fabrice Bellard

quickjs.c

@@ -13397,6 +13397,7 @@ static no_inline __exception int js_unary_arith_slow(JSContext *ctx,
  switch(op) {
  case OP_plus:
  JS_ThrowTypeError(ctx, "bigint argument with unary +");
+ JS_FreeValue(ctx, op1);
  goto exception;
  case OP_inc:
  case OP_dec: