Fixed ability to change image and object layer properties (#4148)

Due to an inverted condition introduced in 629b53c, it
was not actually possible to change properties specific to image layers
and object layers.

Also fixed the undo entry merging for these properties, which was broken
because their undo commands did not have an ID.

Author: bjorn

src/tiled/changeimagelayerproperty.h

@@ -39,6 +39,8 @@ class ChangeImageLayerTransparentColor : public ChangeValue<ImageLayer, QColor>
                                      QList<ImageLayer *> imageLayers,
                                      const QColor &newColor);
 
+    int id() const override { return Cmd_ChangeImageLayerTransparentColor; }
+
 private:
     QColor getValue(const ImageLayer *imageLayer) const override;
     void setValue(ImageLayer *imageLayer, const QColor &value) const override;
@@ -51,6 +53,8 @@ class ChangeImageLayerImageSource : public ChangeValue<ImageLayer, QUrl>
                                 QList<ImageLayer *> imageLayers,
                                 const QUrl &imageSource);
 
+    int id() const override { return Cmd_ChangeImageLayerImageSource; }
+
 private:
     QUrl getValue(const ImageLayer *imageLayer) const override;
     void setValue(ImageLayer *imageLayer, const QUrl &value) const override;

src/tiled/changeobjectgroupproperties.h

@@ -42,6 +42,8 @@ class ChangeObjectGroupColor : public ChangeValue<ObjectGroup, QColor>
                            QList<ObjectGroup *> objectGroups,
                            const QColor &newColor);
 
+    int id() const override { return Cmd_ChangeObjectGroupColor; }
+
 private:
     QColor getValue(const ObjectGroup *objectGroup) const override;
     void setValue(ObjectGroup *objectGroup, const QColor &value) const override;
@@ -61,6 +63,8 @@ class ChangeObjectGroupDrawOrder : public ChangeValue<ObjectGroup, ObjectGroup::
                                QList<ObjectGroup *> objectGroups,
                                ObjectGroup::DrawOrder newDrawOrder);
 
+    int id() const override { return Cmd_ChangeObjectGroupDrawOrder; }
+
 private:
     ObjectGroup::DrawOrder getValue(const ObjectGroup *objectGroup) const override;
     void setValue(ObjectGroup *objectGroup, const ObjectGroup::DrawOrder &value) const override;

src/tiled/propertieswidget.cpp

@@ -1125,7 +1125,7 @@ class LayerProperties : public ObjectProperties
     template <class T>
     QList<T*> selectedLayersOfType(Layer::TypeFlag typeFlag)
     {
-        if (mDocument)
+        if (!mDocument)
             return {};
 
         QList<T*> result;
@@ -1212,9 +1212,8 @@ class ImageLayerProperties : public LayerProperties
             emit mImageProperty->valueChanged();
         if (layerChange.properties & ImageLayerChangeEvent::TransparentColorProperty)
             emit mTransparentColorProperty->valueChanged();
-        if (layerChange.properties & ImageLayerChangeEvent::RepeatProperty) {
+        if (layerChange.properties & ImageLayerChangeEvent::RepeatProperty)
             emit mRepeatProperty->valueChanged();
-        }
     }
 
     ImageLayer *imageLayer() const

src/tiled/undocommands.h

@@ -30,8 +30,10 @@ namespace Tiled {
  */
 enum UndoCommands {
     Cmd_ChangeClassName,
+    Cmd_ChangeImageLayerImageSource,
     Cmd_ChangeImageLayerRepeatX,
     Cmd_ChangeImageLayerRepeatY,
+    Cmd_ChangeImageLayerTransparentColor,
     Cmd_ChangeLayerBlendMode,
     Cmd_ChangeLayerLocked,
     Cmd_ChangeLayerName,
@@ -54,6 +56,8 @@ enum UndoCommands {
     Cmd_ChangeMapStaggerAxis,
     Cmd_ChangeMapStaggerIndex,
     Cmd_ChangeMapTileSize,
+    Cmd_ChangeObjectGroupColor,
+    Cmd_ChangeObjectGroupDrawOrder,
     Cmd_ChangeSelectedArea,
     Cmd_ChangeTileImageRect,
     Cmd_ChangeTileProbability,