protect Widget._style_sheet_changed from being called before _control exists

also ensure _control attributes start out as None, rather than undefined

IPython/frontend/qt/console/console_widget.py

@@ -137,7 +137,12 class ConsoleWidget(LoggingConfigurable, QtGui.QWidget):
     font_changed = QtCore.Signal(QtGui.QFont)
 
     #------ Protected class variables ------------------------------------------
-
+    
+    # control handles
+    _control = None
+    _page_control = None
+    _splitter = None
+    
     # When the control key is down, these keys are mapped.
     _ctrl_down_remap = { QtCore.Qt.Key_B : QtCore.Qt.Key_Left,
                          QtCore.Qt.Key_F : QtCore.Qt.Key_Right,
@@ -182,8 +187,6 class ConsoleWidget(LoggingConfigurable, QtGui.QWidget):
         layout = QtGui.QStackedLayout(self)
         layout.setContentsMargins(0, 0, 0, 0)
         self._control = self._create_control()
-        self._page_control = None
-        self._splitter = None
         if self.paging in ('hsplit', 'vsplit'):
             self._splitter = QtGui.QSplitter()
             if self.paging == 'hsplit':

IPython/frontend/qt/console/ipython_widget.py

@@ -533,12 +533,14 class IPythonWidget(FrontendWidget):
         """ Set the style sheets of the underlying widgets.
         """
         self.setStyleSheet(self.style_sheet)
-        self._control.document().setDefaultStyleSheet(self.style_sheet)
-        if self._page_control:
+        if self._control is not None:
+            self._control.document().setDefaultStyleSheet(self.style_sheet)
+            bg_color = self._control.palette().window().color()
+            self._ansi_processor.set_background_color(bg_color)
+        
+        if self._page_control is not None:
             self._page_control.document().setDefaultStyleSheet(self.style_sheet)
 
-        bg_color = self._control.palette().window().color()
-        self._ansi_processor.set_background_color(bg_color)
 
 
     def _syntax_style_changed(self):