Fix UserControl _build() call (#52)

Author: FeodorFitsner

sdk/python/flet/control.py

@@ -333,7 +333,6 @@ def build_update_commands(self, index, added_controls, commands, isolated=False)
                 for h in current_ints[b1:b2]:
                     # add
                     ctrl = hashes[h]
-                    ctrl._build()
                     innerCmds = ctrl.get_cmd_str(
                         index=index, added_controls=added_controls
                     )
@@ -351,7 +350,6 @@ def build_update_commands(self, index, added_controls, commands, isolated=False)
                 # add
                 for h in current_ints[b1:b2]:
                     ctrl = hashes[h]
-                    ctrl._build()
                     innerCmds = ctrl.get_cmd_str(
                         index=index, added_controls=added_controls
                     )
@@ -380,6 +378,8 @@ def _remove_control_recursively(self, index, control):
     # private methods
     def get_cmd_str(self, indent=0, index=None, added_controls=None):
 
+        self._build()
+
         # remove control from index
         if self.__uid and index != None and self.__uid in index:
             del index[self.__uid]