fix: don't list versions of unused partitions

drive.inc

@@ -79,7 +79,8 @@ function version_from_partnum
     local partnum="$2"
     version="$(parted -m "$drive" -- print|awk -F: \
         -v partnum="$partnum" \
-        '{if (NR > 2 && $1 == partnum) {
+        '{if (NR > 2 && $1 == partnum && $1 >= 2 && $1 <= 4 &&
+                        $6 != "root unused") {
              print $6
          }}')"
     version="$(echo "$version"|cut -d\  -f2)"

tests/drive.sh

@@ -25,6 +25,7 @@ function test_partitioning()
 
     find_unused "$img"
     assertEquals "find_unused" 3 "$unused"
+    assertEquals "version_from_partnum unused" "" "$unused"
 
     rename_partition "$img" 3 "root $min_version"
     find_oldest "$img"