Possible bug + correction for SectionStack dropline position resolution

[klausv]

Hello,

I think I found some bug in the SectionStack code when dragging something onto it.

When dragging something over a sectionstack with an opened section, not all droplines get displayed if you hover below an opened section.

I included a slightly modified SectionsReorderSample.java from the showcase (Accordeon / Sections; Drag Reorder) with an additional canvas to drag around and some more sections below the HTML flow section. When hovering the canvas below the opened HTML flow, no drop lines shows up, they only reappear when you hover near the end of the sectionstack.

I've peeked into the SectionStack.js of the underlying SmartClient, and I think I've found the culprit.
in SectionStack.js, ~ line 503, in getStackDropPosition(), the size variable for the currently inspected member gets set after it is used to check if the member is near the drop position:

            if (memberIsVisible || (member == section)) {
                if (coord < (totalSize + (size/2))) {
                    // respect an explicit canDropBefore setting, which prevents dropping before a
                    // member
                    if (member.canDropBefore === false) return false;
                    return i;
                }
                
                var size = this.memberSizes[visibleMemberCount];
                totalSize += size + this.membersMargin + this.getMemberGap(member);
                visibleMemberCount++;
            }

When I move the size assignment up in front of its first usage, the effect goes away and the droplines behave as expected:

            if (memberIsVisible || (member == section)) {
                var size = this.memberSizes[visibleMemberCount];  // <- moved here
                if (coord < (totalSize + (size/2))) {
                    // respect an explicit canDropBefore setting, which prevents dropping before a
                    // member
                    if (member.canDropBefore === false) return false;
                    return i;
                }
                
                totalSize += size + this.membersMargin + this.getMemberGap(member);
                visibleMemberCount++;
            }

Greetings,
Klaus

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