Use specifically set statistic size over len of statistic values.

nomad/metainfo/search_extension.py

@@ -190,5 +190,6 @@ class Search(Elastic):
     def statistic_values(self, values):
         self._statistic_values = values
         if self._statistic_values is not None:
+            if self.statistic_fixed_size is None:
                 self.statistic_size = len(self._statistic_values)
             self.statistic_fixed_size = len(self._statistic_values)