psppire-output-view: Properly render the first few items of output.

Commit 18f9e37c8bc5 (psppire-output-view: Only render output items once the
window is realized.) fixed a crashing bug, but when I tested it I didn't
carefully look at the output.  In fact, any output items that were rendered
before the window was realized were not displayed, because the widgets
created for them were never shown or properly initialized.  This commit
fixes the problem.

Reported by Adam Zammit.
Bug #43362.