#625 Changes Error Message when trying to reuse stream

src/Microsoft.AspNetCore.WebUtilities/MultipartReaderStream.cs

@@ -226,7 +226,7 @@ public override int Read(byte[] buffer, int offset, int count)
             PositionInnerStream();
             if (!_innerStream.EnsureBuffered(_boundary.FinalBoundaryLength))
             {
-                throw new IOException("Unexpected end of stream.");
+                throw new IOException("Unexpected end of Stream, the content may have already been read by another component. ");
             }
             var bufferedData = _innerStream.BufferedData;
 
@@ -280,7 +280,7 @@ public override async Task<int> ReadAsync(byte[] buffer, int offset, int count,
             PositionInnerStream();
             if (!await _innerStream.EnsureBufferedAsync(_boundary.FinalBoundaryLength, cancellationToken))
             {
-                throw new IOException("Unexpected end of stream.");
+                throw new IOException("Unexpected end of Stream, the content may have already been read by another component. ");
             }
             var bufferedData = _innerStream.BufferedData;