UI: prevent settlement modal when there is nothing to settle (Total 0)

**Detailed Description**
When settlement amount adds up to 0 then modal says that you cannot settle because you're a net receiver

**Actual Behavior**
When totals from such a generation amount to 0
Then show an alert informing the user that there is nothing to settle with the current selection

Steps to reproduce the behavior:
1. Go to '...'
2. Click on '....'
3. Scroll down to '....'

**Expected Behavior**
A clear and concise description of what you expected to happen.

**Environment:**
- Java: [e.g. OpenJDK 11.0.4]
- Node: [e.g. v12.9.1-x86]
- OS: [e.g. Ubuntu 18.04]
- Version: [e.g. 1.0.1]

**Additional Context**
Add any other context about the problem here. Attach any logs here, if applicable.