Only trigger property callback on close if there is 1 or more

Also document this usecase

Signed-off-by: falkTX <falktx@falktx.com>

common/JackEngine.cpp

@@ -773,11 +773,12 @@ int JackEngine::ClientCloseAux(int refnum, bool wait)
         }
     }
 
-    fMetadata.RemoveProperties(NULL, uuid);
-    /* have to do the notification ourselves, since the client argument
-       to fMetadata->RemoveProperties() was NULL
-     */
-    PropertyChangeNotify(uuid, NULL, PropertyDeleted);
+    if (fMetadata.RemoveProperties(NULL, uuid) > 0) {
+        /* have to do the notification ourselves, since the client argument
+          to fMetadata->RemoveProperties() was NULL
+        */
+        PropertyChangeNotify(uuid, NULL, PropertyDeleted);
+    }
 
     // Notify running clients
     NotifyRemoveClient(client->GetClientControl()->fName, refnum);
@@ -912,8 +913,12 @@ int JackEngine::PortUnRegister(int refnum, jack_port_id_t port_index)
         const jack_uuid_t uuid = jack_port_uuid_generate(port_index);
         if (!jack_uuid_empty(uuid))
         {
-            fMetadata.RemoveProperties(NULL, uuid);
-            PropertyChangeNotify(uuid, NULL, PropertyDeleted);
+            if (fMetadata.RemoveProperties(NULL, uuid) > 0) {
+                /* have to do the notification ourselves, since the client argument
+                   to fMetadata->RemoveProperties() was NULL
+                */
+                PropertyChangeNotify(uuid, NULL, PropertyDeleted);
+            }
         }
 
         if (client->GetClientControl()->fActive) {

common/jack/metadata.h

@@ -194,6 +194,18 @@ typedef enum {
         PropertyDeleted
 } jack_property_change_t;
 
+/**
+ * Prototype for the client supplied function that is called by the
+ * engine anytime a property or properties have been modified.
+ *
+ * Note that when the key is empty, it means all properties have been
+ * modified. This is often used to indicate that the removal of all keys.
+ *
+ * @param subject The subject the change relates to, this can be either a client or port
+ * @param key The key of the modified property (URI string)
+ * @param change Wherever the key has been created, changed or deleted
+ * @param arg pointer to a client supplied structure
+ */
 typedef void (*JackPropertyChangeCallback)(jack_uuid_t            subject,
                                            const char*            key,
                                            jack_property_change_t change,