Better error when opening a non-wallet file

Also window modality fixes for __init__.py

gui/qt/__init__.py

@@ -134,7 +134,7 @@ class ElectrumGui:
         try:
             storage = WalletStorage(filename)
         except Exception as e:
-            QMessageBox.information(None, _('Error'), str(e), _('OK'))
+            WindowModalDialog.warning(None, _('Error'), str(e))
             return
         if not storage.file_exists:
             recent = self.config.get('recently_open', [])
@@ -147,7 +147,7 @@ class ElectrumGui:
                 wallet = Wallet(storage)
             except BaseException as e:
                 traceback.print_exc(file=sys.stdout)
-                QMessageBox.warning(None, _('Warning'), str(e), _('OK'))
+                WindowModalDialog.warning(None, _('Warning'), str(e))
                 return
             action = wallet.get_action()
         # run wizard

lib/wallet.py

@@ -69,11 +69,11 @@ class WalletStorage(PrintError):
         except:
             try:
                 d = ast.literal_eval(data)  #parse raw data from reading wallet file
+                labels = d.get('labels', {})
             except Exception as e:
                 raise IOError("Cannot read wallet file '%s'" % self.path)
             self.data = {}
             # In old versions of Electrum labels were latin1 encoded, this fixes breakage.
-            labels = d.get('labels', {})
             for i, label in labels.items():
                 try:
                     unicode(label)