fix reviews on awschunking and default behavior

Author: kai-ion

src/aws-cpp-sdk-core/include/smithy/client/features/ChunkingInterceptor.h

@@ -38,19 +38,20 @@ class AwsChunkedStreamBuf : public std::streambuf {
         if (gptr() < egptr()) {
             return traits_type::to_int_type(*gptr());
         }
-      
-        if (m_stream->good()) {
-            m_stream->read(m_data.GetUnderlyingData(), m_bufferSize);
-            size_t bytesRead = static_cast<size_t>(m_stream->gcount());
-            writeChunk(bytesRead);
-            
-            if ((m_stream->peek() == EOF || m_stream->eof()) && !m_stream->bad()) {
-                writeTrailerToUnderlyingStream();
-            }
-        }
 
+        // Only read from source stream if chunking stream is empty
         if ((m_chunkingStream->peek() == EOF || m_chunkingStream->eof()) && !m_chunkingStream->bad()) {
-            return traits_type::eof();
+            if (m_stream->good()) {
+                m_stream->read(m_data.GetUnderlyingData(), m_bufferSize);
+                size_t bytesRead = static_cast<size_t>(m_stream->gcount());
+                writeChunk(bytesRead);
+                
+                if ((m_stream->peek() == EOF || m_stream->eof()) && !m_stream->bad()) {
+                    writeTrailerToUnderlyingStream();
+                }
+            } else {
+                return traits_type::eof();
+            }
         }
 
         m_chunkingStream->read(m_buffer, sizeof(m_buffer));