AK2: fix insert_line wc/ash bad number error when missing file

tools/ak2-core.sh

@@ -384,7 +384,7 @@ insert_line() {
       after) offset=1;;
     esac;
     line=$((`grep -n "$4" $1 | head -n1 | cut -d: -f1` + offset));
-    if [ "$(wc -l $1 | cut -d\  -f1)" -lt "$line" ]; then
+    if [ -f $1 ] && [ "$(wc -l $1 | cut -d\  -f1)" -lt "$line" ]; then
       echo "$5" >> $1;
     else
       sed -i "${line}s;^;${5}\n;" $1;