fix: assert if transfers are frozen before calling unfreezeTransfers

this assertion is required by the smart contracts

Author: Victor Wiebe

src/contract_wrappers/tokens/__tests__/security_token_wrapper.test.ts

@@ -2032,7 +2032,7 @@ describe('SecurityTokenWrapper', () => {
       // Mock web3 wrapper owner
       when(mockedWrapper.getAvailableAddressesAsync()).thenResolve([expectedOwnerResult]);
 
-      const expectedFrozenResult = false;
+      const expectedFrozenResult = true;
       // Mocked method
       const mockedFrozenMethod = mock(MockedCallMethod);
       // Stub the method

src/contract_wrappers/tokens/security_token_wrapper.ts

@@ -1152,7 +1152,7 @@ export default class SecurityTokenWrapper extends ERC20TokenWrapper {
 
   public unfreezeTransfers = async (params: TxParams) => {
     await this.checkOnlyOwner(params.txData);
-    assert.assert(!(await this.transfersFrozen()), 'Transfers are not frozen');
+    assert.assert((await this.transfersFrozen()), 'Transfers are not frozen');
     return (await this.contract).unfreezeTransfers.sendTransactionAsync(params.txData, params.safetyFactor);
   };