Decode side-band channel number as unsigned integer

This field is unsigned in the protocol, so treat it
as such when we report the channel number in errors.

Change-Id: I20a52809c7a756e9f66b3557a4300ae1e11f6d25
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

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

@@ -148,7 +148,7 @@ class SideBandInputStream extends InputStream {
 				return;
 			}
 
-			channel = rawIn.read();
+			channel = rawIn.read() & 0xff;
 			available -= HDR_SIZE; // length header plus channel indicator
 			if (available == 0)
 				continue;