fix(consensus/XDPoS,core): fix verifyheaders parent lookups for epoch switches#2276

gzliudan wants to merge 1 commit intoXinFinOrg:v2.6.x-betaXinFinOrg/XDPoSChain:v2.6.x-betafrom

gzliudan:fix-verifyheadersgzliudan/XDPoSChain:fix-verifyheadersCopy head branch name to clipboard