Nav: Tweak/fixed popup positioning when using nav without the io.NavMovesMouse flag (it was always assuming a mouse cursor and allocating space for it) (#787)

Note that this bit include badly hardcoded sizes, expecting an improvement later.

imgui.cpp

@@ -5647,7 +5647,11 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
         if ((flags & ImGuiWindowFlags_Tooltip) != 0 && !window_pos_set_by_api && !window_is_child_tooltip)
         {
             ImVec2 ref_pos = (!g.NavDisableHighlight && g.NavDisableMouseHover) ? NavCalcPreferredMousePos() : g.IO.MousePos;
-            ImRect rect_to_avoid(ref_pos.x - 16, ref_pos.y - 8, ref_pos.x + 24, ref_pos.y + 24); // FIXME: Completely hard-coded. Store boxes in mouse cursor data? Scale? Center on cursor hit-point?
+            ImRect rect_to_avoid;
+            if (!g.NavDisableHighlight && g.NavDisableMouseHover && !g.IO.NavMovesMouse)
+                rect_to_avoid = ImRect(ref_pos.x - 16, ref_pos.y - 8, ref_pos.x + 16, ref_pos.y + 8); 
+            else
+                rect_to_avoid = ImRect(ref_pos.x - 16, ref_pos.y - 8, ref_pos.x + 24, ref_pos.y + 24); // FIXME-NAV: Completely hard-coded based on expected mouse cursor size. Store boxes in mouse cursor data? Scale? Center on cursor hit-point?
             window->PosFloat = FindBestWindowPosForPopup(ref_pos, window->Size, &window->AutoPosLastDirection, rect_to_avoid);
             if (window->AutoPosLastDirection == ImGuiDir_None)
                 window->PosFloat = ref_pos + ImVec2(2,2); // If there's not enough room, for tooltip we prefer avoiding the cursor at all cost even if it means that part of the tooltip won't be visible.