fix BufferedInputStream.read regression

In commit 7fffba2, I had modified BufferedInputStream.read to keep
reading until in.available() <= 0 or an EOF was reached, but neglected
to update the offset into the destination buffer after each read.
This caused the previously-read data to be overwritten.  This commit
fixes that regression.

classpath/java/io/BufferedInputStream.java

@@ -66,6 +66,7 @@ public class BufferedInputStream extends InputStream {
         }
         break;
       } else {
+        offset += c;
         count += c;
         length -= c;