Comment 16 for bug 1843059

Fixes have merged for

- the output of the query for detecting existing amphora images is not properly checked so empty output is used in subsequent calls which leads to invalid commands
- we do not check that the contents of stdout for command output to see if it is non-empty before using it in key places

The last one in #c15 should close the bug.

Serves me right for filing an omnibus bug even if they were small issues.