v.external.out: Fix Resource Leak Issue in list.c

[ShubhamDesai]

This pull request fixes issue identified by Coverity Scan (CID : 1207810)

[nilason]

This one is a pure false positive. list is allocated (in format_list()) only if len > 0, which is checked in line 78. We might try to satisfy the Analyser with the added check of list (L78):

    if (list && len > 0) {

[ShubhamDesai]

This one is a pure false positive. list is allocated (in format_list()) only if len > 0, which is checked in line 78. We might try to satisfy the Analyser with the added check of list (L78):

    if (list && len > 0) {

Done