dApp: handle quick pay case that user has not enough service tokens

## Description

This refers to the cases `f)` and `g)` in [this image](https://github.com/raiden-network/light-client/issues/2882#issuecomment-914412357). For the first version of the quick pay feature in #2882 this was skipped. This means when this case happens, the payment fails.

## Acceptance criteria
- 

## Tasks
- [ ] 
