quiltimport: fix misquoting of parsed -p<num> parameter

Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-quiltimport.sh

@@ -129,7 +129,7 @@ do
 	fi
 
 	if [ -z "$dry_run" ] ; then
-		git apply --index -C1 $level "$tmp_patch" &&
+		git apply --index -C1 ${level:+"$level"} "$tmp_patch" &&
 		tree=$(git write-tree) &&
 		commit=$( (echo "$SUBJECT"; echo; cat "$tmp_msg") | git commit-tree $tree -p $commit) &&
 		git update-ref -m "quiltimport: $patch_name" HEAD $commit || exit 4