RangeSelect/MultiSelect: Box-select: fixed "when dragging from void" implementation messing with calling BeginMultiSelect() without a selection size.

imgui_widgets.cpp

@@ -7537,17 +7537,22 @@ void ImGui::MultiSelectItemFooter(ImGuiID id, bool* p_selected, bool* p_pressed)
             const bool rect_overlap_curr = bs->BoxSelectRectCurr.Overlaps(g.LastItemData.Rect);
             const bool rect_overlap_prev = bs->BoxSelectRectPrev.Overlaps(g.LastItemData.Rect);
             if ((rect_overlap_curr && !rect_overlap_prev && !selected) || (rect_overlap_prev && !rect_overlap_curr))
+            {
+                if (storage->LastSelectionSize <= 0 && bs->IsStartedFromVoid)
+                {
+                    pressed = true; // First item act as a pressed: code below will emit selection request and set NavId (whatever we emit here will be overridden anyway)
+                }
+                else
                 {
                     selected = !selected;
                     ImGuiSelectionRequest req = { ImGuiSelectionRequestType_SetRange, selected, item_data, item_data };
                     ImGuiSelectionRequest* prev_req = (ms->IO.Requests.Size > 0) ? &ms->IO.Requests.Data[ms->IO.Requests.Size - 1] : NULL;
-                if (storage->LastSelectionSize == 0 && bs->IsStartedFromVoid)
+                    if (prev_req && prev_req->Type == ImGuiSelectionRequestType_SetRange && prev_req->RangeLastItem == ms->BoxSelectLastitem && prev_req->Selected == selected)
-                    pressed = true; // First item act as a pressed: code below will emit selection request and set NavId (whatever we emit here will be overriden anyway)
-                else if (prev_req && prev_req->Type == ImGuiSelectionRequestType_SetRange && prev_req->RangeLastItem == ms->BoxSelectLastitem && prev_req->Selected == selected)
                         prev_req->RangeLastItem = item_data; // Merge span into same request
                     else
                         ms->IO.Requests.push_back(req);
-                storage->LastSelectionSize++;
+                }
+                storage->LastSelectionSize = ImMax(storage->LastSelectionSize + 1, 1);
             }
             ms->BoxSelectLastitem = item_data;
         }