Ensure CPU mining is reliable
Ensure CPU mining is reliable

Summary: Generating an extra nonce in the coinbase may lead to have an undersized coinbasewhen CPU mining.

Test Plan: Repeatedly use generatetoaddress RPC call.

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D2073

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