try to make impress support going before start

openlp/plugins/presentations/lib/impresscontroller.py

@@ -493,9 +493,13 @@ class ImpressDocument(PresentationDocument):
         """
         Triggers the previous slide on the running presentation.
         """
+        # if we are at the presentations start don't go further back, just return True
+        if self.slide_ended_reverse and self.get_slide_number() == 1:
+            return True
         self.slide_ended = False
         self.slide_ended_reverse = False
         self.control.gotoPreviousEffect()
+        return False
 
     def get_slide_text(self, slide_no):
         """

openlp/plugins/presentations/lib/messagelistener.py

@@ -191,18 +191,18 @@ class Controller(object):
         """
         log.debug('Live = {live}, previous'.format(live=self.is_live))
         if not self.doc:
-            return
+            return False
         if not self.is_live:
-            return
+            return False
         if self.hide_mode:
             if not self.doc.is_active():
-                return
+                return False
             if self.doc.slidenumber > 1:
                 self.doc.slidenumber -= 1
                 self.poll()
-            return
+            return False
         if not self.activate():
-            return
+            return False
         ret = self.doc.previous_step()
         self.poll()
         print('previous returning: %d' % ret)