(fix) make sure our heartbeat interval is always greater than the internal one

ActiveSync/SOGoActiveSyncDispatcher.m

@@ -2039,6 +2039,9 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     }
   else
     {
+      if (heartbeatInterval < internalInterval)
+        heartbeatInterval = internalInterval; 
+
       status = 1;
     }