8358183: [JVMCI] crash accessing nmethod::jvmci_name in CodeCache::aggregate

Reviewed-by: thartmann
Backport-of: 74822ce12acaf9816aa49b75ab5817ced3710776

Author: Boris Ulasevich

src/hotspot/share/code/codeBlob.cpp

@@ -210,6 +210,8 @@ void CodeBlob::purge() {
   if (_mutable_data != blob_end()) {
     os::free(_mutable_data);
     _mutable_data = blob_end(); // Valid not null address
+    _mutable_data_size = 0;
+    _relocation_size = 0;
   }
   if (_oop_maps != nullptr) {
     delete _oop_maps;

src/hotspot/share/code/nmethod.cpp

@@ -2166,6 +2166,7 @@ void nmethod::purge(bool unregister_nmethod) {
   }
   CodeCache::unregister_old_nmethod(this);
 
+  JVMCI_ONLY( _metadata_size = 0; )
   CodeBlob::purge();
 }