cancel virtual backups if none of the jobids contains files

[pstorz]

Virtual backups consolidating jobids that contain no files failed when creating the bootstrap file.
This PR now checks for the number of files before creating the bootstrap file and cancels the consolidation if no files exist.

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[arogge]

I think it is OK to consolidate a job with no files. The problem is consolidating a job with files that were purged.
So we should fail if one or more of the jobs had its files purged.

[arogge]

data() does not guarantee a null-terminated string. You'll need c_str() for that.
The const_cast<> is also not needed, as strchr is defined to be char* strchr(const char *s, int c); so it should happily accept the const char* that c_str() will return.

Suggested change

	p = strchr(const_cast<char*>(jobids.data()), ','); /* find oldest jobid */
	p = strchr(jobids.c_str(), ','); /* find oldest jobid */

[arogge]

at second thought: all of this pointer trickery is used, because we get a comma-separated list of jobids in a string and we need the first and the last of these.
I propose to have a function vector<std::string> split_string(const std::string& str, const std:string& delim) that splits str at delim and puts the pieces into a vector it returns.
We can then simply do:

auto jobid_list = split_string(jobids, ',');
jcr->impl->previous_jr = JobDbRecord{};
jcr->impl->previous_jr.JobId = str_to_int64(jobid_list.front.c_str());

and further below

jcr->impl->previous_jr = JobDbRecord{};
jcr->impl->previous_jr.JobId = str_to_int64(jobid_list.back.c_str());

[arogge]

I updated the PR branch with my personal version of choice. We now detect if one of the jobs that should be consolidated had its files pruned or was removed from the catalog (by means of prune, purge or delete) and fail in that case only.

Done