Made AsyncAppenderBase.isQueueBelowDiscardingThreshold public to fa…

…cilitate reporting loss of log events in a health check. (#325)

Co-authored-by: Erik van Oosten <[email protected]>

logback-core/src/main/java/ch/qos/logback/core/AsyncAppenderBase.java

@@ -166,7 +166,7 @@ protected void append(E eventObject) {
         put(eventObject);
     }
 
-    private boolean isQueueBelowDiscardingThreshold() {
+    public boolean isQueueBelowDiscardingThreshold() {
         return (blockingQueue.remainingCapacity() < discardingThreshold);
     }