fix htpasswd/htdbm brown paper bag bugs

- use the correct string to generate the hash from. PR 54735
- print error message instead of empty string

while there, replace strdup + check for oom with apr_pstrdup


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1465115 13f79535-47bb-0310-9956-ffa450edef68