Remove useless assignment to local variable

https://github.com/Tenacom/Louis/security/code-scanning/30

src/Louis/IO/ReadOnlyMemoryStream.cs

@@ -646,7 +646,6 @@ private int EmulateRead(int count)
 
     private void CopyToInternal(Stream destination, int originalPosition)
     {
-        var remaining = _position - originalPosition;
 #if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
         // On runtimes that have Stream.Write(ReadOnlySpan<byte>), just use that.
         destination.Write(_data.Span[originalPosition.._position]);
@@ -656,6 +655,7 @@ private void CopyToInternal(Stream destination, int originalPosition)
         // Fortunately, MemoryMarshal can tell us whether this is the case
         // and provide us with a reference to the array and the starting index
         // of the ReadOnlyMemory, sparing us the use of ArrayPool for a temporary array.
+        var remaining = _position - originalPosition;
         if (MemoryMarshal.TryGetArray(_data, out var dataArray))
         {
             // If our data is actually in an array, write directly from that.