[io grant] Be explicit what IO::Handle.opened returns

for unopened handles.

Author: zoffixznet

doc/Type/IO/Handle.pod6

@@ -505,7 +505,7 @@ Defined as:
 
     method opened(IO::Handle:D: --> Bool:D)
 
-Returns C<True> if the handle is open.
+Returns C<True> if the handle is open, C<False> otherwise.
 
 =head2 method t