Prevents Bounty from being claimed twice (#1374)

* signing prefix added

* Minor improvement

* Tests changed

* Successfully tested

* Minor improvements

* Minor improvements

* Revert "Dangling commas are now required. (#1359)"

This reverts commit a6889776f4.

* updates

* fixes #1356

* Removed extra semicolon.

contracts/bounties/BreakInvariantBounty.sol

@@ -45,6 +45,7 @@ contract BreakInvariantBounty is PullPayment, Ownable {
    * @param target contract
    */
   function claim(Target target) public {
+    require(!_claimed);
     address researcher = _researchers[target];
     require(researcher != address(0));
     // Check Target contract invariants

test/BreakInvariantBounty.test.js

@@ -90,6 +90,10 @@ contract('BreakInvariantBounty', function ([_, owner, researcher, anyone, nonTar
             it('no longer accepts rewards', async function () {
               await assertRevert(ethSendTransaction({ from: owner, to: this.bounty.address, value: reward }));
             });
+
+            it('reverts when reclaimed', async function () {
+              await assertRevert(this.bounty.claim(this.target.address, { from: researcher }));
+            });
           });
         });
       });