Fix open() with binary flag

Signed-off-by: Moritz Lenz <moritz@faui2k3.org>

src/core/IO.pm

@@ -210,7 +210,7 @@ sub open($filename, :$r, :$w, :$a, :$bin) {
     unless pir::istrue__IP($PIO) {
         fail("Unable to open file '$filename'");
     }
-    $PIO.encoding('utf8');
+    $PIO.encoding($bin ?? 'binary' !! 'utf8');
     IO.new(:$PIO)
 }