Template generator includes tspend that overspends treasury

[matheusd]

This makes the generated template not be accepted during its final check and thus the block template cannot be created.

This is only an issue on simnet, where the treasury has a balance that is lower than the maximum spendable during its first policy window.

Sample log line of the failure:

 [TRC] MINR: NewBlockTemplate: failed to do final check for check connect block when making new block template: block contains a TSpend that has an in valid expenditure: treasury balance may not become negative: balance 3431726972864 spend 4100000005100 

(I can probably address this in a few days).