Fix going to next/previous frame/image

sloth/annotations/model.py

@@ -53,7 +53,7 @@ class ModelItem:
         p = self.parent()
         if p is not None:
             row = p.getPosOfChild(self)
-            if row < len(p.children()) - 2:
+            if row < len(p.children()) - 1:
                 return p.getChildAt(row+1)
         return None
 

sloth/core/labeltool.py

@@ -250,16 +250,16 @@ class LabelTool(QObject):
         return self._model
 
     def gotoNext(self):
-        # TODO move this to the scene
         if self._model is not None and self._current_image is not None:
             next_image = self._current_image.getNextSibling()
-            self.setCurrentImage(next_image)
+            if next_image is not None:
+                self.setCurrentImage(next_image)
 
     def gotoPrevious(self):
-        # TODO move this to the scene
         if self._model is not None and self._current_image is not None:
             prev_image = self._current_image.getPreviousSibling()
-            self.setCurrentImage(prev_image)
+            if prev_image is not None:
+                self.setCurrentImage(prev_image)
 
     def updateModified(self):
         """update all GUI elements which depend on the state of the model,