Qt: couple of general PySide6 fixes

scripts/joinmarket-qt.py

@@ -2020,8 +2020,14 @@ class JMMainWindow(QMainWindow):
         pp_field.setEnabled(False)
         use_pp = QCheckBox('Input Mnemonic Extension', self)
         use_pp.setCheckState(QtCore.Qt.CheckState(False))
-        use_pp.stateChanged.connect(lambda state: pp_field.setEnabled(state
-            == QtCore.Qt.Checked))
+
+        def _use_pp_state_changed(state):
+            checked = Qt.CheckState(state) == QtCore.Qt.Checked
+            pp_field.setEnabled(checked)
+            if not checked:
+                pp_field.clear()
+
+        use_pp.stateChanged.connect(_use_pp_state_changed)
         pp_hbox.addWidget(use_pp)
         pp_hbox.addWidget(pp_field)
 

scripts/qtsupport.py

@@ -155,7 +155,7 @@ async def JMQtMessageBox(parent, msg, mbtype='info', title='',
     title = "JoinmarketQt - " + title
     result_fut = asyncio.get_event_loop().create_future()
 
-    class JMQtDMessageBox(QMessageBox, QtCore.QObject):
+    class JMQtDMessageBox(QMessageBox):
 
         def __init__(self, parent):
             QMessageBox.__init__(self, parent=parent)
@@ -360,8 +360,8 @@ def make_password_dialog(self, msg):
     grid.setColumnStretch(1, 1)
     #TODO perhaps add an icon here
     logo = QLabel()
-    lockfile = ":icons/lock.png"
-    logo.setPixmap(QPixmap(lockfile).scaledToWidth(36))
+    lock_icon = QIcon.fromTheme(QIcon.ThemeIcon.DialogPassword)
+    logo.setPixmap(lock_icon.pixmap(QtCore.QSize(48, 48)))
     logo.setAlignment(QtCore.Qt.AlignCenter)
 
     grid.addWidget(logo, 0, 0)