[perl #91508] __DATA__ starts reading on the next line

[perl #91508] __DATA__ starts reading on the next line

In pod/perldata it is described that the DATA filehandle starts
reading after the __DATA__ token. In reality, it starts reading on the
line following the __DATA__ token.

Example:

print while <DATA>; __DATA__ foo
bar

This prints "bar", not "foo\nbar".

The attached patch fixes the documentation in pod/perldata.pod.