Initialize public_blob in Ed25519 key.
Initialize public_blob in Ed25519 key.

Was removed earlier (because the 'initialization'
of first impl was at END of method and thus broke
main impl of cert loading) but neglected to add
back to TOP of __init__, so broken anytime there
is no cert in play.

Fixes #1071

ameily/paramiko,mirrorcoder/paramiko,jaraco/paramiko,paramiko/paramiko