Fix search entry after editing the toolbar

[b4n]

According to b0b0ebb we guard against proxying the widget more than once for some Windows reasons, but this breaks the case where the same GeanyEntryAction has to re-create a fresh proxy, like when moving the item around.

So, move the guard value to the proxied widget, not the action.

Fixes #3831.

As this is Windows-related (see b0b0ebb), it could be nice if somebody could actually check that this patch doesn't break anything there. I likely won't, at least in a yearly manner.

[ntrel]

Looks good, thanks. Tested on Linux, works.

[eht16]

Tested on Linux and Windows, works perfectly.

I don't remember the initial problems from 12 years ago, maybe it was GTK2 releated or a bug in early GTK3 versions or so.

[b4n]

I don't remember the initial problems from 12 years ago, maybe it was GTK2 releated or a bug in early GTK3 versions or so.

Any chance you could try removing the guard and see if anything weird happens? Not that I remember any details about that though, only Git does remember anything :)

[b4n]

@eht16 I merged this anyway, but feel free to still check whether the shenanigans are still useful 😉

[eht16]

It seems to work without the guard as well.
The connect_proxy function is called four times here, but it's the same on Linux and Windows and in either way, the search toolbar item still works after re-ordering.

Since we cannot reproduce this anymore and the "fix" is so long ago, maybe it was really related to some Windows-GTK2 bugginess.