qt init: make sure wallet file parsing errors are shown in gui

Some exceptions were just killing the gui silently and not even logged.

E.g.:
```
E | gui.qt.ElectrumGui | error loading wallet (or creating window for it)
Traceback (most recent call last):
  File "/opt/electrum/electrum/gui/qt/__init__.py", line 433, in main
    if not self.start_new_window(path, self.config.get('url'), app_is_starting=True):
  File "/opt/electrum/electrum/gui/qt/__init__.py", line 307, in wrapper
    return func(self, *args, **kwargs)
  File "/opt/electrum/electrum/gui/qt/__init__.py", line 332, in start_new_window
    wallet = self._start_wizard_to_select_or_create_wallet(path)
  File "/opt/electrum/electrum/gui/qt/__init__.py", line 377, in _start_wizard_to_select_or_create_wallet
    db = WalletDB(storage.read(), manual_upgrades=False)
  File "/opt/electrum/electrum/wallet_db.py", line 73, in __init__
    self.load_data(raw)
  File "/opt/electrum/electrum/wallet_db.py", line 104, in load_data
    self._after_upgrade_tasks()
  File "/opt/electrum/electrum/wallet_db.py", line 202, in _after_upgrade_tasks
    self._load_transactions()
  File "/opt/electrum/electrum/util.py", line 439, in <lambda>
    return lambda *args, **kw_args: do_profile(args, kw_args)
  File "/opt/electrum/electrum/util.py", line 435, in do_profile
    o = func(*args, **kw_args)
  File "/opt/electrum/electrum/wallet_db.py", line 1310, in _load_transactions
    self.data = StoredDict(self.data, self, [])
  File "/opt/electrum/electrum/json_db.py", line 79, in __init__
    self.__setitem__(k, v)
  File "/opt/electrum/electrum/json_db.py", line 44, in wrapper
    return func(self, *args, **kwargs)
  File "/opt/electrum/electrum/json_db.py", line 97, in __setitem__
    v = self.db._convert_dict(self.path, key, v)
  File "/opt/electrum/electrum/wallet_db.py", line 1361, in _convert_dict
    v = dict((k, SwapData(**x)) for k, x in v.items())
```

electrum/gui/qt/__init__.py

@@ -324,22 +324,15 @@ class ElectrumGui(BaseElectrumGui, Logger):
                                parent=None,
                                title=_('Error'),
                                text=_('Cannot load wallet') + ' (1):\n' + repr(e))
-            # if app is starting, still let wizard to appear
+            # if app is starting, still let wizard appear
             if not app_is_starting:
                 return
-        if not wallet:
-            try:
-                wallet = self._start_wizard_to_select_or_create_wallet(path)
-            except (WalletFileException, BitcoinException) as e:
-                self.logger.exception('')
-                custom_message_box(icon=QMessageBox.Warning,
-                                   parent=None,
-                                   title=_('Error'),
-                                   text=_('Cannot load wallet') + ' (2):\n' + repr(e))
-        if not wallet:
-            return
-        # create or raise window
         try:
+            if not wallet:
+                wallet = self._start_wizard_to_select_or_create_wallet(path)
+            if not wallet:
+                return
+            # create or raise window
             for window in self.windows:
                 if window.wallet.storage.path == wallet.storage.path:
                     break
@@ -350,7 +343,7 @@ class ElectrumGui(BaseElectrumGui, Logger):
             custom_message_box(icon=QMessageBox.Warning,
                                parent=None,
                                title=_('Error'),
-                               text=_('Cannot create window for wallet') + ':\n' + repr(e))
+                               text=_('Cannot load wallet') + '(2) :\n' + repr(e))
             if app_is_starting:
                 wallet_dir = os.path.dirname(path)
                 path = os.path.join(wallet_dir, get_new_wallet_name(wallet_dir))