Bugfix: basename of schedule file path is a tuple in new Qt

Previous to this commit, selecting a new schedule file would
not "correctly" detect that an unfinished tumble run was selected
(note that this "detection" is currently just checking the
name of the file, so it may have to be changed in future). The
reason for the failure to detect is that in the PyQt5 version,
the filenames are returned as a tuple, and so the str() conversion
did not match.

scripts/joinmarket-qt.py

@@ -370,7 +370,7 @@ class SpendTab(QWidget):
         else:
             w.statusBar().showMessage("Schedule loaded OK.")
             self.spendstate.loaded_schedule = schedule
-            self.spendstate.schedule_name = os.path.basename(str(firstarg))
+            self.spendstate.schedule_name = os.path.basename(str(firstarg[0]))
             self.updateSchedView()
             if self.spendstate.schedule_name == "TUMBLE.schedule":
                 reply = JMQtMessageBox(self, "An incomplete tumble run detected. "