Fixed bug in reading Flux from Channel

Fixed bug where the returned Flux from DataBufferUtils.read() would be
completed prematurely if the channel was not ready to read, but did
not reach the end of the file either.

spring-core/src/main/java/org/springframework/core/io/buffer/DataBufferUtils.java

@@ -164,7 +164,7 @@ public abstract class DataBufferUtils {
 			try {
 				ByteBuffer byteBuffer = ByteBuffer.allocate(chunkSize);
 				int read;
-				if ((read = channel.read(byteBuffer)) > 0) {
+				if ((read = channel.read(byteBuffer)) >= 0) {
 					byteBuffer.flip();
 					boolean release = true;
 					DataBuffer dataBuffer = this.dataBufferFactory.allocateBuffer(read);