Change getUnicodeStream encoding from UTF-8 to UTF-16.

The JDBC standard requires two-bytes encoding to be returned from
getUnicodeStream.

Author: nicktorwald

src/main/java/org/tarantool/jdbc/SQLResultSet.java

@@ -295,7 +295,8 @@ public InputStream getAsciiStream(String columnLabel) throws SQLException {
 
     @Override
     public InputStream getUnicodeStream(int columnIndex) throws SQLException {
-        return new ByteArrayInputStream(getString(columnIndex).getBytes(Charset.forName("UTF-8")));
+        String string = getString(columnIndex);
+        return string == null ? null : new ByteArrayInputStream(string.getBytes(Charset.forName("UTF-16")));
     }
 
     @Override