QPID-8518: [Broker-J] Message transfer freezes when session runs out of transfer frames

This closes #83
diff --git a/broker-plugins/amqp-1-0-protocol/src/main/java/org/apache/qpid/server/protocol/v1_0/AMQPConnection_1_0.java b/broker-plugins/amqp-1-0-protocol/src/main/java/org/apache/qpid/server/protocol/v1_0/AMQPConnection_1_0.java
index 665ee0a..10a907d 100644
--- a/broker-plugins/amqp-1-0-protocol/src/main/java/org/apache/qpid/server/protocol/v1_0/AMQPConnection_1_0.java
+++ b/broker-plugins/amqp-1-0-protocol/src/main/java/org/apache/qpid/server/protocol/v1_0/AMQPConnection_1_0.java
@@ -44,7 +44,7 @@
 
     String CONNECTION_SESSION_CREDIT_WINDOW_SIZE = "connection.sessionCreditWindowSize";
     @ManagedContextDefault(name = CONNECTION_SESSION_CREDIT_WINDOW_SIZE)
-    int DEFAULT_CONNECTION_SESSION_CREDIT_WINDOW_SIZE = 8192;
+    int DEFAULT_CONNECTION_SESSION_CREDIT_WINDOW_SIZE = 2 * 8192;
 
     String SEND_SASL_FINAL_CHALLENGE_AS_CHALLENGE = "connection.sendSaslFinalResponseAsChallenge";
     @ManagedContextDefault(name = SEND_SASL_FINAL_CHALLENGE_AS_CHALLENGE)
diff --git a/broker-plugins/amqp-1-0-protocol/src/main/java/org/apache/qpid/server/protocol/v1_0/AbstractReceivingLinkEndpoint.java b/broker-plugins/amqp-1-0-protocol/src/main/java/org/apache/qpid/server/protocol/v1_0/AbstractReceivingLinkEndpoint.java
index f346dbe..86fda5b 100644
--- a/broker-plugins/amqp-1-0-protocol/src/main/java/org/apache/qpid/server/protocol/v1_0/AbstractReceivingLinkEndpoint.java
+++ b/broker-plugins/amqp-1-0-protocol/src/main/java/org/apache/qpid/server/protocol/v1_0/AbstractReceivingLinkEndpoint.java
@@ -173,6 +173,10 @@
                     _currentDelivery = null;
                 }
             }
+            else
+            {
+                getSession().sendFlowConditional();
+            }
         }
         else
         {