Quick fix to avoid a tight loop when processing added blocks in txpool (besu-eth#6309)

Signed-off-by: Fabio Di Fabio <fabio.difabio@consensys.net>
Signed-off-by: jflo <justin+github@florentine.us>

Author: fab-10

ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/transactions/TransactionPool.java

@@ -359,6 +359,13 @@ public void onBlockAdded(final BlockAddedEvent event) {
                       } finally {
                         blockAddedLock.unlock();
                       }
+                    } else {
+                      try {
+                        // wait a bit before retrying
+                        Thread.sleep(100);
+                      } catch (InterruptedException e) {
+                        throw new RuntimeException(e);
+                      }
                     }
                   }
                   return null;