fix #1144, focus window on macOS

[jinjiaodawang]

Fix #1144: In macOS, when opening sioyek in full-screen mode, opening a file can still focus on the window

[ahrm]

Can you see why the original focus code here does not work?

sioyek/pdf_viewer/main.cpp

Line 851 in 8ae1f79

if (!nofocus) {

.

Your code doesn't handle some cases (e.g. when --nofocus is passed as an argument).

[jinjiaodawang]

It seems that when running ./sioyek file.pdf --nofocus, this part of the code ensures that the window does not gain focus. However, when I open the file from the file browser, the code will directly run the handle_args function by emitting file_ready through OpenWithApplication.
(

sioyek/pdf_viewer/main.cpp

Lines 848 to 850 in 7181c5a

	QObject::connect(&app, &OpenWithApplication::file_ready, [&main_widget](const QString& file_name) {
	handle_args(QStringList() << QCoreApplication::applicationFilePath() << file_name);
	});

)
In other words, the judgment of --nofocus will only be invoked when running in the terminal.
But you are correct that --nofocus is ignored.

[jinjiaodawang]

We could move the judgement of --nofocus inside handle_args. You may reject my PR, or I fix it in that way if you perfer.

[ahrm]

We should probably handle it inside file_ready after running handle_args (not inside handle_args). Thanks for your efforts.