Fix traceback when going live with presentation while blanked to desktop

openlp/plugins/presentations/lib/messagelistener.py

@@ -243,6 +243,10 @@ class Controller(object):
         Instruct the controller to stop and hide the presentation.
         """
         log.debug('Live = %s, stop' % self.is_live)
+        # The document has not been loaded yet, so don't do anything. This can happen when going live with a 
+        # presentation while blanked to desktop.
+        if not self.doc:
+            return
         # Save the current slide number to be able to return to this slide if the presentation is activated again.
         if self.doc.is_active():
             self.doc.slidenumber = self.doc.get_slide_number()

openlp/plugins/presentations/lib/powerpointcontroller.py

@@ -330,6 +330,7 @@ class PowerpointDocument(PresentationDocument):
             """
             log.debug('start_presentation')
             # SlideShowWindow measures its size/position by points, not pixels
+            # https://technet.microsoft.com/en-us/library/dn528846.aspx
             try:
                 dpi = win32ui.GetActiveWindow().GetDC().GetDeviceCaps(88)
             except win32ui.error:

openlp/plugins/presentations/lib/presentationtab.py

@@ -128,7 +128,8 @@ class PresentationTab(SettingsTab):
                       'Clicking on a selected slide in the slidecontroller advances to next effect.'))
         self.ppt_window_check_box.setText(
             translate('PresentationPlugin.PresentationTab',
-                      'Let PowerPoint control the size and position of the presentation window.'))
+                      'Let PowerPoint control the size and position of the presentation window '
+                      '(workaround for Windows 8 scaling issue).'))
         self.pdf_program_check_box.setText(
             translate('PresentationPlugin.PresentationTab', 'Use given full path for mudraw or ghostscript binary:'))