fix: check for disposal before updating the issue cache (#658)

This change adds a check to see if the `SnykLanguageClient` has been disposed before processing diagnostics. This prevents potential errors or unexpected behavior if the client is no longer active.  It's a good defensive programming practice to avoid operating on a disposed object.

src/main/kotlin/snyk/common/lsp/SnykLanguageClient.kt

@@ -105,6 +105,7 @@ class SnykLanguageClient :
         diagnosticsParams: PublishDiagnosticsParams,
         scanPublisher: SnykScanListenerLS
     ) {
+        if (disposed) return
         val snykFile = SnykFile(project, filePath.toVirtualFile())
         val firstDiagnostic = diagnosticsParams.diagnostics.firstOrNull()
         val product = firstDiagnostic?.source