prevent panic when receiving malformed LSP PublishDiagnostic (#2160)

Instead of panicing we can discard the malformed diagnostic. This
`.parse()` fails commonly when a non-conformant language server gives
a diagnostic with a location that breaks the spec:

    { "character": 0, "line": -1 }

can currently be returned by ElixirLS and the python LS. Other
messages in this block are discarded but this one feels special enough
to log.

0 files changed, 0 insertions, 0 deletions