Fix isFinished in sequentialcommandgroup.py

- isFinished is false after command is finished
See allwpilib#7901 [here](wpilibsuite/allwpilib#7901)

Author: reecelikesramen

Diff for: commands2/sequentialcommandgroup.py

@@ -86,7 +86,7 @@ def end(self, interrupted: bool):
         self._currentCommandIndex = -1
 
     def isFinished(self) -> bool:
-        return self._currentCommandIndex == len(self._commands)
+        return self._currentCommandIndex == len(self._commands) or self._currentCommandIndex == -1
 
     def runsWhenDisabled(self) -> bool:
         return self._runsWhenDisabled