Clipper: accept that no item have been submitted if in indeterminate …

…Begin(INT_MAX) mode. (#1311, #3823)

imgui.cpp

@@ -3062,7 +3062,8 @@ static bool ImGuiListClipper_StepInternal(ImGuiListClipper* clipper)
         bool affected_by_floating_point_precision = ImIsFloatAboveGuaranteedIntegerPrecision(clipper->StartPosY) || ImIsFloatAboveGuaranteedIntegerPrecision(window->DC.CursorPos.y);
         if (affected_by_floating_point_precision)
             clipper->ItemsHeight = window->DC.PrevLineSize.y + g.Style.ItemSpacing.y; // FIXME: Technically wouldn't allow multi-line entries.
-
+        if (clipper->ItemsHeight == 0.0f && clipper->ItemsCount == INT_MAX) // Accept that no item have been submitted if in indeterminate mode.
+            return false;
         IM_ASSERT(clipper->ItemsHeight > 0.0f && "Unable to calculate item height! First item hasn't moved the cursor vertically!");
         calc_clipping = true;   // If item height had to be calculated, calculate clipping afterwards.
     }