Viewports: fixed misuse of inset_max.y, which typically would have broken using BeginViewportSideBar() with ImGuiDir_Down, regression from 1.91.0. (#7940, #7823)

Amend cfd23957f

imgui_internal.h

@@ -2003,7 +2003,7 @@ struct ImGuiViewportP : public ImGuiViewport
 
     // Calculate work rect pos/size given a set of offset (we have 1 pair of offset for rect locked from last frame data, and 1 pair for currently building rect)
     ImVec2  CalcWorkRectPos(const ImVec2& inset_min) const                           { return ImVec2(Pos.x + inset_min.x, Pos.y + inset_min.y); }
-    ImVec2  CalcWorkRectSize(const ImVec2& inset_min, const ImVec2& inset_max) const { return ImVec2(ImMax(0.0f, Size.x - inset_min.x - inset_max.x), ImMax(0.0f, Size.y - inset_min.y + inset_max.y)); }
+    ImVec2  CalcWorkRectSize(const ImVec2& inset_min, const ImVec2& inset_max) const { return ImVec2(ImMax(0.0f, Size.x - inset_min.x - inset_max.x), ImMax(0.0f, Size.y - inset_min.y - inset_max.y)); }
     void    UpdateWorkRect()            { WorkPos = CalcWorkRectPos(WorkInsetMin); WorkSize = CalcWorkRectSize(WorkInsetMin, WorkInsetMax); } // Update public fields
 
     // Helpers to retrieve ImRect (we don't need to store BuildWorkRect as every access tend to change it, hence the code asymmetry)