Checks if stream is actually pollable. Some classes may implement
GPollableInputStream but have only certain instances of that class
be pollable. If this method returns FALSE, then the behavior of
other GPollableInputStream methods is undefined.
For any given stream, the value returned by this method is constant;
a stream cannot switch from pollable to non-pollable or vice versa.
Since 2.28
Checks if stream is actually pollable. Some classes may implement GPollableInputStream but have only certain instances of that class be pollable. If this method returns FALSE, then the behavior of other GPollableInputStream methods is undefined. For any given stream, the value returned by this method is constant; a stream cannot switch from pollable to non-pollable or vice versa. Since 2.28