common: improve performance of find_cached_package

find_cached_package was unnecessarily looping over all packages which
uses a lot of CPU and could be exceptionally slow when PKGDEST contains
a lot of packages.

Fix this by adding the target pkgname, pkgver and arch to the glob and
only process potential candidates.

lib/common.sh

@@ -146,7 +146,7 @@ find_cached_package() {
 		[[ -d $dir ]] || continue
 
 		shopt -s extglob nullglob
-		mapfile -t packages < <(printf "%s\n" "$dir"/*.pkg.tar?(.!(sig|*.*)))
+		mapfile -t packages < <(printf "%s\n" "$dir"/${targetname}-${targetver}-*${targetarch}.pkg.tar?(.!(sig|*.*)))
 		shopt -u extglob nullglob
 
 		for pkg in "${packages[@]}"; do