State hash calculation is interrupted and forcing node stopping sync in non-"FullState" mode

[superboyiii]

Describe the bug
When setting FullState as false in StateService.json of StateService, that will not store every MPT data, but just calculate the latest State Root hash. However, I find it can be interrupted and throw exception which can force node stopping sync. But it works well when set FullState as true.

To Reproduce
Steps to reproduce the behavior:

1. Prepare a testnet node, install MPTTrie and StateService
2. Set FullState as false in StateService.json of StateService
3. Run the node, wait for sometime.
4. Error will be showed as:
   

Expected behavior
Every State Root hash should be calculated correctly and be the same as FullState mode. It shouldn't be interrupted. It shouldn't stop node sync as well.

Screenshots

Platform:
winx64, neo master branch
@cschuchardt88 @shargon