getHexGasTotal and increaseLastGasPrice now gracefully handle null and undefined values

ui/app/helpers/utils/confirm-tx.util.js

@@ -13,7 +13,7 @@ import {
 import { unconfirmedTransactionsCountSelector } from '../../selectors/confirm-transaction'
 
 export function increaseLastGasPrice (lastGasPrice) {
-  return ethUtil.addHexPrefix(multiplyCurrencies(lastGasPrice, 1.1, {
+  return ethUtil.addHexPrefix(multiplyCurrencies(lastGasPrice || '0x0', 1.1, {
     multiplicandBase: 16,
     multiplierBase: 10,
     toNumericBase: 'hex',
@@ -28,7 +28,7 @@ export function hexGreaterThan (a, b) {
 }
 
 export function getHexGasTotal ({ gasLimit, gasPrice }) {
-  return ethUtil.addHexPrefix(multiplyCurrencies(gasLimit, gasPrice, {
+  return ethUtil.addHexPrefix(multiplyCurrencies(gasLimit || '0x0', gasPrice || '0x0', {
     toNumericBase: 'hex',
     multiplicandBase: 16,
     multiplierBase: 16,