jp (common): fixed empty table display when headers are specified

frontends/src/jp/common.py

@@ -555,6 +555,10 @@ class Table(object):
                     raise exceptions.DataError(u'rows size is not coherent')
             self.rows.append(new_row)
 
+        if not data and headers is not None:
+            # the table is empty, we print headers at their lenght
+            self.sizes = [len(h) for h in headers]
+
     @staticmethod
     def readDictValues(data, keys, defaults=None):
         if defaults is None: