Improve borrower withdrawal checks

[xrchz]

From Discord:

So far I'm tracking two potential changes on the withdrawal function for borrowers: 1. include staked RPL when checking the debt is not exceeded by funds available and 2. disallow withdrawing when "defaulted debt" i.e. debt in expired pools, exists

knoshua — Today at 13:42
Yes, 1+2 is what I'm asking for I think