Fix disabling gtk_doc (merged from upstream).

breakage reported by tb@

devel/libpeas/patches/patch-meson_build

@@ -0,0 +1,17 @@
+From 1be9b5a51ca4200d9cff69642368c24225b58dd5 Mon Sep 17 00:00:00 2001
+From: Matt Turner <mattst88@gmail.com>
+Date: Mon, 21 Mar 2022 19:13:04 -0700
+Subject: [PATCH] meson: Fix disabling gtk_doc
+
+Index: meson.build
+--- meson.build.orig
++++ meson.build
+@@ -251,7 +251,7 @@ configure_file(
+ )
+ 
+ # Options
+-build_gtk_doc = gi_docgen_dep.found()
++build_gtk_doc = get_option('gtk_doc') and gi_docgen_dep.found()
+ 
+ install_glade_catalog = get_option('glade_catalog')
+ if install_glade_catalog and not gladeui_dep.found()