GtLockDB: fixed a few issues where the connection to the db was not instantiated yet

Signed-off-by: Nicola Vigano <nicola.vigano@esrf.fr>

zUtil_DataStructures/GtLockDB.m

@@ -21,6 +21,8 @@ classdef GtLockDB < handle
             obj.filename  = filename;
             obj.filetable = filetable;
             obj.hasLock   = false;
+
+            gtDBConnect();
         end
 
         function acquire(obj, timeout)