HeapArray: Fix swap() not swapping size

Even though it's not used.

src/common/heap_array.h

@@ -247,7 +247,11 @@ public:
 
   void fill(const_reference value) { std::fill(begin(), end(), value); }
 
-  void swap(this_type& move) { std::swap(m_data, move.m_data); }
+  void swap(this_type& rhs)
+  {
+    std::swap(m_data, rhs.m_data);
+    std::swap(m_size, rhs.m_size);
+  }
 
   void resize(size_t new_size) { internal_resize(new_size, m_data, m_size); }