8238961: Assertion failure in new field layout code when ContendedPad…

…dingWidth == 0

Reviewed-by: hseigel, coleenp

src/hotspot/share/classfile/fieldLayoutBuilder.cpp

@@ -353,7 +353,7 @@ void FieldLayout::fill_holes(const InstanceKlass* super_klass) {
   // If the super class has @Contended annotation, a padding block is
   // inserted at the end to ensure that fields from the subclasses won't share
   // the cache line of the last field of the contended class
-  if (super_klass->has_contended_annotations()) {
+  if (super_klass->has_contended_annotations() && ContendedPaddingWidth > 0) {
     LayoutRawBlock* p = new LayoutRawBlock(LayoutRawBlock::PADDING, ContendedPaddingWidth);
     p->set_offset(b->offset() + b->size());
     b->set_next_block(p);