Merge "Check connection's error stream before reading from it"

org.eclipse.jgit/src/org/eclipse/jgit/transport/AmazonS3.java

@@ -512,10 +512,14 @@ public class AmazonS3 {
 			final HttpURLConnection c) throws IOException {
 		final IOException err = new IOException(MessageFormat.format(JGitText.get().amazonS3ActionFailed
 				, action, key, HttpSupport.response(c), c.getResponseMessage()));
+		final InputStream errorStream = c.getErrorStream();
+		if (errorStream == null)
+			return err;
+
 		final ByteArrayOutputStream b = new ByteArrayOutputStream();
 		byte[] buf = new byte[2048];
 		for (;;) {
-			final int n = c.getErrorStream().read(buf);
+			final int n = errorStream.read(buf);
 			if (n < 0)
 				break;
 			if (n > 0)