abuild: filter out empty lines when scanning for SO dependencies

This works around a bug in busybox 1.22.0 that makes 'grep -w ^' hang.
It is triggered when there are no deps. (eg. musl)

abuild.in

@@ -1077,7 +1077,7 @@ scan_shared_objects() {
 
 	# now find the so dependencies
 	scanelf --nobanner --recursive --needed "$datadir"  | tr ' ' ':' \
-		| awk -F ":" '$1 == "ET_DYN" || $1 == "ET_EXEC" {print $2}'  \
+		| awk -F ":" '$2 != "" && ($1 == "ET_DYN" || $1 == "ET_EXEC") {print $2}'  \
 		| sed 's:,:\n:g' | sort -u \
 	| while read soname; do
 		# only add files that are not self provided