bitcoin-spv - ValidateSPV.validateHeaderChain does not completely validate input  Won't Fix
`ValidateSPV.validateHeaderChain` takes as input a sequence of Bitcoin headers and calculates the total accumulated difficulty across the entire sequence. The input headers are checked to ensure they are relatively well-formed:\\n```\\n// Check header chain length\\nif (\\_headers.length % 80 != 0) {return ERR\\_BAD\\_LENGTH;}\\n```\\n\\nHowever, the function lacks a check for nonzero length of `_headers`. Although the total difficulty returned would be zero, an explicit check would make this more clear.
If `headers.length` is zero, return `ERR_BAD_LENGTH`
```\\n// Check header chain length\\nif (\\_headers.length % 80 != 0) {return ERR\\_BAD\\_LENGTH;}\\n```\\n