Guard optional clientInfo + fix empty filename in diagnostics for scanner errors

[ajax16384]

Diagnostics for scanner errors were published with a broken URI

Two independent fixes found while running pasls against mixed Delphi/FPC
projects, both reproduced with plain LSP clients (no editor).

1. Guard optional clientInfo in ShowConfigStatus

clientInfo is optional in the LSP spec and TClientInfo.version is not
auto-created. A minimal client that omits clientInfo crashed the server
right on initialize. Now both are checked; the client line logs as
[unspecified] when absent.

2. Empty filename in diagnostics for scanner errors

Symptom: for files whose first error comes from the scanner (e.g.
{$I ../../x.inc} that cannot be resolved → EScannerError, error code 1003),
the client never received any publishDiagnostics — the file silently looked
"clean or dead", while stderr showed the error.

Root cause: in TSourceParser.ParseSource the except branch passed the
filename through

with FParser.CurSourcePos do
  FOnError(Self, E.Message, FileName, aCode, Row, Column);

For scanner errors the parser never advanced, so CurSourcePos is still
(Row=0, Column=0, FileName='') — and its empty FileName shadowed the
filled local Filename. The diagnostic ended up in
TPublishDiagnostics.Add(fileName='') → uri = 'file:', which no client can
match to a document, so the publish was dropped.

Fixes:

• ParseSource except: drop the with-statement, pass the local Filename
  explicitly, read Row/Column directly from CurSourcePos.
• DoError (multi-error path): same shadowing pattern — fall back to the
  buffer filename when CurSourcePos.FileName is empty.

Result: scanner errors (unresolvable includes, etc.) are now reported with a
valid document URI instead of being silently dropped.

Related upstream fixes

While testing pasls diagnostics, two parser bugs in its dependencies were found
and fixed upstream:

• fcl-passrc (FPC, merged): an empty const section in a class declaration
  (e.g. strict private const with no constants, or an {$IFDEF}-gutted one)
  broke TPasParser with Expected "=", so StrictSyntaxCheck failed on
  valid units —
  https://gitlab.com/freepascal.org/fpc/source/-/merge_requests/1567
• Lazarus CodeTools (MR open): an empty inactive branch
  ({$IFDEF X}...{$ELSE}{$ENDIF}) left an orphan { in CleanedSrc, so
  Explore reported "unexpected end of source" on valid code —
  https://gitlab.com/freepascal.org/lazarus/lazarus/-/merge_requests/775