rewrite get incomplete backups code

Signed-off-by: Nico Schottelius <nico@kr.ethz.ch>

ccollect

@@ -425,13 +425,14 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
    #
    # Check incomplete backups (needs echo to remove newlines)
    #
-   ls -1 | grep "${CMARKER}\$" > "${TMP}" || \
-      _exit_err "Cannot list incomplete files"
+   ls -1 | grep "${CMARKER}\$" > "${TMP}"; ret=$?
 
+   if [ "$ret" -eq 0 ]; then
       _techo "Incomplete backups: $(echo $(cat "${TMP}"))"
       if [ -f "${c_delete_incomplete}" ]; then
          delete_from_file "${TMP}" "${CMARKER}"
       fi
+   fi
 
    #
    # Check: maximum number of backups is reached?