fix(util): open lock file in append mode to avoid overwriting files

Previously if we opened a lock on an existing file with useful content
we overwrote it with an empty file. This is obviously not desired, hence
open the file handle in append mode preserving its content.

Signed-off-by: Levente Polyak <anthraxx@archlinux.org>

src/lib/common.sh

@@ -135,7 +135,7 @@ lock() {
 	# Only reopen the FD if it wasn't handed to us
 	if ! [[ "/dev/fd/$1" -ef "$2" ]]; then
 		mkdir -p -- "$(dirname -- "$2")"
-		eval "exec $1>"'"$2"'
+		eval "exec $1>>"'"$2"'
 	fi
 
 	if ! flock -n "$1"; then