fix #314854: element offset marked nostyle after edit

Resolves: https://musescore.org/en/node/314854

Currently, on any drag operation in edit mode
(including "drag" via arrow keys, which uses the same code),
the offset is set to NOSTYLE, whereas it should be UNSTYLED
(if it was previously styled).
The result is that after such an edit, the offset can no longer
be reset to its original STYLED state,
so it even after a reset of the offset itself,
it remains marked as NOSTYLE and will not respond to style changes,

There is code in the ordinary drag case (Element::endDrag())
to handle this, but it is missing from the edit mode version.
The fix here is to simply reproduce that code in Element::endEditDrag().

libmscore/element.cpp

@@ -2099,9 +2099,9 @@ QVector<QLineF> Element::genericDragAnchorLines() const
       if (parent()->isSegment()) {
             System* system = toSegment(parent())->measure()->system();
             const int stIdx = staffIdx();
-            yp = system->staffCanvasYpage(stIdx);
+            yp = system ? system->staffCanvasYpage(stIdx) : 0.0;
             if (placement() == Placement::BELOW)
-                  yp += system->staff(stIdx)->bbox().height();
+                  yp += system ? system->staff(stIdx)->bbox().height() : 0.0;
             //adjust anchor Y positions to staffType offset
             if (staff())
                 yp += staff()->staffTypeForElement(this)->yoffset().val()* spatium();
@@ -2191,7 +2191,10 @@ void Element::endEditDrag(EditData& ed)
       if (eed) {
             for (const PropertyData &pd : qAsConst(eed->propertyData)) {
                   setPropertyFlags(pd.id, pd.f); // reset initial property flags state
-                  if (score()->undoPropertyChanged(this, pd.id, pd.data))
+                  PropertyFlags f = pd.f;
+                  if (f == PropertyFlags::STYLED)
+                        f = PropertyFlags::UNSTYLED;
+                  if (score()->undoPropertyChanged(this, pd.id, pd.data, f))
                         changed = true;
                   }
             eed->propertyData.clear();