refactor transfer funds to voucher

contracts/VoucherHub.sol

@@ -174,13 +174,10 @@ contract VoucherHub is
         // The proxy contract does a delegatecall to its implementation.
         // Re-Entrancy safe because the target contract is controlled.
         Voucher(voucherAddress).initialize(owner, address(this), expiration, voucherType);
-        // SRLC
-        if (!IERC20($._iexecPoco).transfer(voucherAddress, value)) {
-            revert("VoucherHub: SRLC transfer to voucher failed");
-        }
         _mint(voucherAddress, value); // VCHR
         $._isVoucher[voucherAddress] = true;
         emit VoucherCreated(voucherAddress, owner, voucherType, expiration, value);
+        _transfertFundsToVoucher($._iexecPoco, voucherAddress, value); // SRLC
     }
 
     /**
@@ -193,10 +190,7 @@ contract VoucherHub is
         VoucherHubStorage storage $ = _getVoucherHubStorage();
         require($._isVoucher[voucher], "VoucherHub: unknown voucher");
         _mint(voucher, value); // VCHR
-        if (!IERC20($._iexecPoco).transfer(voucher, value)) {
-            // SRLC
-            revert("VoucherHub: SRLC transfer to voucher failed");
-        }
+        _transfertFundsToVoucher($._iexecPoco, voucher, value); // SRLC
         uint256 expiration = block.timestamp + $.voucherTypes[Voucher(voucher).getType()].duration;
         Voucher(voucher).setExpiration(expiration);
         emit VoucherToppedUp(voucher, expiration, value);