This fixes crashes that we see of the form

# Problematic frame:
# V  [libjvm.so+0x7745a8]  G1CollectedHeap::allocate_new_tlab(unsigned long, unsigned long, unsigned long*)+0xb8

The problem is that if the memory region isn't fully initialized,
then further attempts to manipulate it, specifically top()
in HeapRegion::par_allocate_impl(), will end up dereferencing NULL.

--- a/src/hotspot/share/gc/g1/g1AllocRegion.inline.hpp	Wed Oct 14 18:49:42 2020
+++ b/src/hotspot/share/gc/g1/g1AllocRegion.inline.hpp	Wed Nov  6 08:09:08 2024
@@ -82,6 +82,12 @@
   HeapRegion* alloc_region = _alloc_region;
   assert_alloc_region(alloc_region != NULL, "not initialized properly");
 
+  // if we are null then we will SEGV later
+  // return NULL and let the caller retry or cleanup
+  if (alloc_region == NULL) {
+    return NULL;
+  }
+
   HeapWord* result = par_allocate(alloc_region, min_word_size, desired_word_size, actual_word_size);
   if (result != NULL) {
     trace("alloc", min_word_size, desired_word_size, *actual_word_size, result);