Fix accounting for new/delete from different threads for VariableContext::Thread

MemoryTracker assumes that for VariableContext::Thread new/delete may be
called from different threads, hence the amount of memory can go
negative.

However the MemoryTracker is nested, so even if the negative amount is
allowed for VariableContext::Thread it does not allowed for anything
upper, and hence the MemoryTracking will not be decremented properly.

Fix this, by passing initial size to the parent free.

This should fix memory drift for HTTP queries.

src/Common/MemoryTracker.cpp

@@ -210,14 +210,15 @@ void MemoryTracker::free(Int64 size)
         DB::TraceCollector::collect(DB::TraceType::MemorySample, StackTrace(), -size);
     }
 
+    Int64 accounted_size = size;
     if (level == VariableContext::Thread)
     {
         /// Could become negative if memory allocated in this thread is freed in another one
-        amount.fetch_sub(size, std::memory_order_relaxed);
+        amount.fetch_sub(accounted_size, std::memory_order_relaxed);
     }
     else
     {
-        Int64 new_amount = amount.fetch_sub(size, std::memory_order_relaxed) - size;
+        Int64 new_amount = amount.fetch_sub(accounted_size, std::memory_order_relaxed) - accounted_size;
 
         /** Sometimes, query could free some data, that was allocated outside of query context.
           * Example: cache eviction.
@@ -228,7 +229,7 @@ void MemoryTracker::free(Int64 size)
         if (unlikely(new_amount < 0))
         {
             amount.fetch_sub(new_amount);
-            size += new_amount;
+            accounted_size += new_amount;
         }
     }
 
@@ -236,7 +237,7 @@ void MemoryTracker::free(Int64 size)
         loaded_next->free(size);
 
     if (metric != CurrentMetrics::end())
-        CurrentMetrics::sub(metric, size);
+        CurrentMetrics::sub(metric, accounted_size);
 }