Handle IO exceptions in adapter shutdown.

Author: kinyoklion

lib/sdk/server/src/main/java/com/launchdarkly/sdk/server/DataSourceSynchronizerAdapter.java

@@ -90,15 +90,19 @@ public CompletableFuture<FDv2SourceResult> next() {
     }
 
     @Override
-    public void close() throws IOException {
+    public void close()  {
         synchronized (startLock) {
             if (closed) {
                 return;
             }
             closed = true;
         }
 
-        dataSource.close();
+        try {
+            dataSource.close();
+        } catch (IOException e) {
+            // Ignore as we are shutting down.
+        }
         shutdownFuture.complete(FDv2SourceResult.shutdown());
         if(startFuture != null) {
             // If the start future is done, this has no effect.