fix: clancel futures during failure (#91)

resolves #85

open-vulnerability-clients/src/main/java/io/github/jeremylong/openvulnerability/client/nvd/NvdCveClient.java

@@ -260,13 +260,8 @@ private Future<RateLimitedCall> callApi(int clientIndex, int startIndex) throws
     }
 
     @Override
-    public void close() throws Exception {
-        if (clients != null) {
-            for (RateLimitedClient client : clients) {
-                client.close();
-            }
-            clients = null;
-        }
+    public void close() {
+        indexesToRetrieve.clear();
         if (futures.size() > 0) {
             for (Future<RateLimitedCall> future : futures) {
                 if (!future.isDone()) {
@@ -275,6 +270,16 @@ public void close() throws Exception {
             }
             futures.clear();
         }
+        if (clients != null) {
+            for (RateLimitedClient client : clients) {
+                try {
+                    client.close();
+                } catch (Exception ex) {
+                    LOG.debug("Error closing client during `close`", ex);
+                }
+            }
+            clients = null;
+        }
     }
 
     @Override
@@ -342,13 +347,15 @@ public Collection<DefCveItem> next() {
             }
         } catch (InterruptedException e) {
             Thread.currentThread().interrupt();
+            close();
             throw new NvdApiException(e);
         } catch (ExecutionException e) {
             // in rare cases we get an error from the NVD - log the error and only fail if we retry too many times
             LOG.debug("Error retrieving the NVD data", e);
             if (hasNext()) {
                 return next();
             }
+            close();
             return null;
         }
     }