Sets task's result to error (which task assumes ownership of)
and completes the task (see gio.task.Task.returnPointer for more
discussion of exactly what this means).
Note that since the task takes ownership of error, and since the
task may be completed before returning from gio.task.Task.returnError,
you cannot assume that error is still valid after calling this.
Call glib.error.ErrorG.copy on the error if you need to keep a local copy
as well.
Sets task's result to error (which task assumes ownership of) and completes the task (see gio.task.Task.returnPointer for more discussion of exactly what this means).
Note that since the task takes ownership of error, and since the task may be completed before returning from gio.task.Task.returnError, you cannot assume that error is still valid after calling this. Call glib.error.ErrorG.copy on the error if you need to keep a local copy as well.
See also gio.task.Task.returnNewError, gio.task.Task.returnNewErrorLiteral.