SetKeyboardFocusHere() added assert to prevent passing values smaller than -1 as we may have to outlaw them (I think nobody was using that)

imgui.cpp

@@ -5457,6 +5457,7 @@ void ImGui::SetScrollHere(float center_y_ratio)
 
 void ImGui::SetKeyboardFocusHere(int offset)
 {
+    IM_ASSERT(offset >= -1);    // -1 is allowed but not below
     ImGuiWindow* window = GetCurrentWindow();
     window->FocusIdxAllRequestNext = window->FocusIdxAllCounter + 1 + offset;
     window->FocusIdxTabRequestNext = INT_MAX;