Fixed bug in pop method.

Avoid crash if o is empty.

src/@dates/pop.m

@@ -28,6 +28,10 @@ function o = pop(o, p) % --*-- Unitary tests --*--
 % You should have received a copy of the GNU General Public License
 % along with Dynare.  If not, see <http://www.gnu.org/licenses/>.
 
+if o.isempty()
+    return
+end
+    
 if nargin<2
     % Remove last date
     o.ndat = o.ndat-1;