fix(lsp): handle negative activeSignature in signatureHelp (#17064)

omnisharp-roslyn can send negative values:

    {
      activeParameter = 0,
      activeSignature = -1,
      signatures = { {
          documentation = "",
          label = "TestEntity.TestEntity()",
          parameters = {}
        } }
    }

In 3.16 of the specification `activeSignature` is defined as `uinteger`
and therefore negative values shouldn't be allowed, but within 3.15 it
was defined as `number` which makes me think we can be a bit lenient in
this case and handle them.

The expected behavior is quite clear:

    The active signature. If omitted or the value lies outside the
    range of `signatures` the value defaults to zero or is ignored if
    the `SignatureHelp` has no signatures.

Fixes an error:

    util.lua:1685: attempt to get length of local 'lines' (a nil value)
    util.lua:1685: in function 'trim_empty_lines'
    handlers.lua:334: in function 'textDocument/signatureHelp'

0 files changed, 0 insertions, 0 deletions