Fix nested non-byref like VC with no pointer fields

Author: AaronRobinsonMSFT

src/coreclr/vm/methodtablebuilder.cpp

@@ -8732,29 +8732,30 @@ MethodTableBuilder::HandleExplicitLayout(
     if (pMT->IsByRefLike())
         return CheckByRefLikeValueClassLayout(pMT, pFieldLayout);
 
-    // This method assumes there is a GC desc associated with the MethodTable.
-    _ASSERTE(pMT->ContainsPointers());
-
     // Build a layout of the value class (vc). Don't know the sizes of all the fields easily, but
     // do know (a) vc is already consistent so don't need to check it's overlaps and
     // (b) size and location of all objectrefs. So build it by setting all non-oref
-    // then fill in the orefs later
+    // then fill in the orefs later if present.
     UINT fieldSize = pMT->GetNumInstanceFieldBytes();
 
     CQuickBytes qb;
     bmtFieldLayoutTag *vcLayout = (bmtFieldLayoutTag*) qb.AllocThrows(fieldSize * sizeof(bmtFieldLayoutTag));
     memset((void*)vcLayout, nonoref, fieldSize);
 
-    // use pointer series to locate the orefs
-    CGCDesc* map = CGCDesc::GetCGCDescFromMT(pMT);
-    CGCDescSeries *pSeries = map->GetLowestSeries();
-
-    for (SIZE_T j = 0; j < map->GetNumSeries(); j++)
+    // If the type contains pointers fill it out from the GC data
+    if (pMT->ContainsPointers())
     {
-        CONSISTENCY_CHECK(pSeries <= map->GetHighestSeries());
+        // use pointer series to locate the orefs
+        CGCDesc* map = CGCDesc::GetCGCDescFromMT(pMT);
+        CGCDescSeries *pSeries = map->GetLowestSeries();
 
-        memset((void*)&vcLayout[pSeries->GetSeriesOffset() - OBJECT_SIZE], oref, pSeries->GetSeriesSize() + pMT->GetBaseSize());
-        pSeries++;
+        for (SIZE_T j = 0; j < map->GetNumSeries(); j++)
+        {
+            CONSISTENCY_CHECK(pSeries <= map->GetHighestSeries());
+
+            memset((void*)&vcLayout[pSeries->GetSeriesOffset() - OBJECT_SIZE], oref, pSeries->GetSeriesSize() + pMT->GetBaseSize());
+            pSeries++;
+        }
     }
 
     ExplicitClassTrust explicitClassTrust;