build-system: Don't fail if tarball is there but no dir

The previous code assumed everything was good to go if just the tar ball
was there, but if it wasn't unpacked, it all went sideways.

This makes it more robust and to actually handle that the tarball might
just be there.

Signed-off-by: Anton Lundin <glance@acc.umu.se>

scripts/get-dep-lib.sh

@@ -67,6 +67,9 @@ curl_download_library() {
 
 	if [ ! -f "$filename" ]; then
 		${CURL} "${base_url}${filename}"
+	fi
+
+	if [ ! -d "$name" ] || [ "$name" -ot "$filename" ] ; then
 		rm -rf "$name"
 		mkdir "$name"
 		tar -C "$name" --strip-components=1 -xf "$filename"