Fix annotations menu when loading movie file with --read CLI option

[Perdu]

Issue

When launching libTAS with the --read option to load a movie file (also probably with -w), the annotations menu is greyed out and it is not possible to edit them.

Analysis

In MainWindow.cpp, annotateMovieAction is set to false by default, and only set to true in slotMovieEnable(), called when the user clicks on the checkbox. The case where the checkbox is on when libTAS starts (due to using -w or -r) is not taken into account.

Solution

Instead of setting annotateMovieAction to false by default, we evaluate whether a movie is loaded to set its value. For this, I reused the logic used in updateMovieParams().