Avoid app crashing when amounts are invalid

[alfetopito]

Description

Sometimes totalValue is NaN.

Hard to reproduce bug. Saw this sporadically, not sure what's causing it.

In any way, this change prevents app crashing when totalValue is falsy or NaN.

To Test

Fill in all fields in the deploy form. Sometimes the total value calculation fails.

• [ ] When that happens, the app shouldn't crash.

Background

N/A

[ghost]

Travis automatic deployment:

• 🔐 Safe app link: To be added as a custom app on Safe Multisig Rinkeby, Mainnet or xDai
• 📖 Storybook: Component stories