LibJS: Update mmap name after recycling a HeapBlock :^)

Fixes #7507.

Userland/Libraries/LibJS/Heap/BlockAllocator.cpp

@@ -33,8 +33,16 @@ BlockAllocator::~BlockAllocator()
 
 void* BlockAllocator::allocate_block([[maybe_unused]] char const* name)
 {
-    if (!m_blocks.is_empty())
-        return m_blocks.take_last();
+    if (!m_blocks.is_empty()) {
+        auto* block = m_blocks.take_last();
+#ifdef __serenity__
+        if (set_mmap_name(block, HeapBlock::block_size, name) < 0) {
+            perror("set_mmap_name");
+            VERIFY_NOT_REACHED();
+        }
+#endif
+        return block;
+    }
 
 #ifdef __serenity__
     auto* block = (HeapBlock*)serenity_mmap(nullptr, HeapBlock::block_size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_RANDOMIZED | MAP_PRIVATE, 0, 0, HeapBlock::block_size, name);