qml: tighten self._loading guard to encompass whole loadWallet fn, not just task thread.

Also make sure QEWallet is never instantiated within the task thread.

electrum/gui/qml/qedaemon.py

@@ -168,6 +168,10 @@ class QEDaemon(AuthMixin, QObject):
     @pyqtSlot(str)
     @pyqtSlot(str, str)
     def loadWallet(self, path=None, password=None):
+        if self._loading:
+            return
+        self._loading = True
+
         if path is None:
             self._path = self.daemon.config.get('wallet_path')  # command line -w option
             if self._path is None:
@@ -175,8 +179,11 @@ class QEDaemon(AuthMixin, QObject):
         else:
             self._path = path
         if self._path is None:
+            self._loading = False
             return
 
+        self.loadingChanged.emit()
+
         self._path = standardize_path(self._path)
         self._name = os.path.basename(self._path)
 
@@ -189,12 +196,11 @@ class QEDaemon(AuthMixin, QObject):
         if not password:
             password = self._password
 
-        wallet_already_open = self.daemon.get_wallet(self._path) is not None
+        wallet_already_open = self.daemon.get_wallet(self._path)
+        if wallet_already_open is not None:
+            wallet_already_open_password = QEWallet.getInstanceFor(wallet_already_open).password
 
         def load_wallet_task():
-            self._loading = True
-            self.loadingChanged.emit()
-
             try:
                 local_password = password  # need this in local scope
                 wallet = None
@@ -214,10 +220,10 @@ class QEDaemon(AuthMixin, QObject):
                 if wallet is None:
                     return
 
-                if wallet_already_open:
+                if wallet_already_open is not None:
                     # wallet already open. daemon.load_wallet doesn't mind, but
                     # we need the correct current wallet password below
-                    local_password = QEWallet.getInstanceFor(wallet).password
+                    local_password = wallet_already_open_password
 
                 if self.daemon.config.WALLET_USE_SINGLE_PASSWORD:
                     self._use_single_password = self.daemon.update_password_for_directory(old_password=local_password, new_password=local_password)