libraries/webkit2gtk4.1: Fix -j0 build fails on single-core systems.

Signed-off-by: B. Watson <urchlay@slackware.uk>

Signed-off-by: Willy Sudiarto Raharjo <willysr@slackbuilds.org>

libraries/webkit2gtk4.1/webkit2gtk4.1.SlackBuild

@@ -109,7 +109,9 @@ cd build
 
 # The build might crash on high specs machines because ninja eat all
 # of the resources, so let's try to limit it to half the available ones
-"${NINJA:=ninja}" -j$(expr $(nproc) / 2)
+# 20241016 bkw: make sure we never get -j0, see webkit2gtk.SlackBuild
+# for detailed explanation.
+"${NINJA:=ninja}" -j$(expr '(' $(nproc) + 1 ')' / 2)
 DESTDIR=$PKG $NINJA -j1 install
 
 mkdir -p $PKG/usr/share/gtk-doc/html/webkit{2,dom}gtk-4.1