ref_ratios.size() -> max_level

Address a breaking change in AMReX.

Source/Parallelization/GuardCellManager.cpp

@@ -101,9 +101,9 @@ guardCellManager::Init (
     // the fine grid by a number of cells equal to the ref_ratio in the moving
     // window direction.
     if (do_moving_window) {
-        WARPX_ALWAYS_ASSERT_WITH_MESSAGE(ref_ratios.size() <= 1,
+        WARPX_ALWAYS_ASSERT_WITH_MESSAGE(max_level <= 1,
             "The number of grow cells for the moving window currently assumes 2 levels max.");
-        const auto nlevs = static_cast<int>(ref_ratios.size()+1);
+        const auto nlevs = static_cast<int>(max_level+1);
         const int max_r = (nlevs > 1) ? ref_ratios[0][moving_window_dir] : 2;
 
         ngx = std::max(ngx,max_r);