Fixed buffer allocation size

Author: sakno

src/DotNext.IO/IO/FileReader.cs

@@ -103,7 +103,7 @@ private ref readonly MemoryOwner<byte> EnsureBufferAllocated()
     {
         ref var result = ref buffer;
         if (result.IsEmpty)
-            result = Allocator.AllocateAtLeast(maxBufferSize);
+            result = Allocator.AllocateExactly(maxBufferSize);
 
         Debug.Assert(!result.IsEmpty);
         return ref result;

src/DotNext.IO/IO/FileWriter.cs

@@ -71,7 +71,7 @@ private ref readonly MemoryOwner<byte> EnsureBufferAllocated()
     {
         ref var result = ref buffer;
         if (result.IsEmpty)
-            result = Allocator.AllocateAtLeast(maxBufferSize);
+            result = Allocator.AllocateExactly(maxBufferSize);
 
         Debug.Assert(!result.IsEmpty);
         return ref result;
@@ -108,7 +108,7 @@ public void Produce(int count)
         ArgumentOutOfRangeException.ThrowIfGreaterThan((uint)count, (uint)FreeCapacity, nameof(count));
 
         if (count > 0 && buffer.IsEmpty)
-            buffer = Allocator.AllocateAtLeast(maxBufferSize);
+            buffer = Allocator.AllocateExactly(maxBufferSize);
 
         bufferOffset += count;
     }