Fix range of irreversible blocks to be gathered with <app_name>_context_data_view view

Fix definition of min_block in hivemind_app_context_data_view

Fixes related to crash of hivemind on steem-11.

If some program (in this case hivemind) has been processing data (or was inactive) too long, blocks that should be in hive.irreversible, are no longer there. Missing blocks now are in hive.blocks, because blockchain is producing new blocks, and irreversible block num is going forward. Because of this, min_block in <app_name>_context_data_view was calculated incorrectly, now it should work.