Don't add nonfunctional proxyconfig plugins in the Settings dialog

src/bitmessageqt/settings.py

@@ -57,8 +57,15 @@ class SettingsDialog(QtGui.QDialog):
             pass
         else:
             # Append proxy types defined in plugins
+            # FIXME: this should be a function in mod:`plugin`
             for ep in pkg_resources.iter_entry_points(
                     'bitmessage.proxyconfig'):
+                try:
+                    ep.load()
+                except Exception:  # it should add only functional plugins
+                    # many possible exceptions, which are don't matter
+                    pass
+                else:
                     self.comboBoxProxyType.addItem(ep.name)
 
         self.lineEditMaxOutboundConnections.setValidator(