allow burning even if burning balance <= 0
allow burning even if burning balance <= 0

this allows minting strategies on eth side


Former-commit-id: c832548224e0825a932f57d3f1f663332d8c2475
syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin2,syscoin/syscoin2,syscoin/syscoin