Bug 30367: Skip processing if we don't get releases

Bug 30367: Skip processing if we don't get releases

Some repos don't have releases, and this seems to break things as get returns an empty
response. Calling from_json on this is the error

This simply skips the bad responses to avoid the error:

To test:
1. Have this on your koha-conf.xml file:

 <plugin_repos>
    <repo>
        <name>ByWater Solutions</name>
        <org_name>bywatersolutions</org_name>
        <service>github</service>
    </repo>
    <repo>
        <name>Theke Solutions</name>
        <org_name>thekesolutions</org_name>
        <service>gitlab</service>
    </repo>
    <repo>
        <name>PTFS Europe</name>
        <org_name>ptfs-europe</org_name>
        <service>github</service>
    </repo>
 </plugin_repos>

2. Restart all services:
   $ restart_all
3. Search for the term 'barclaycard'

The search will give an error:

malformed JSON string, neither tag, array, object, number, string or atom, at character offset 0 (before "(end of string)") at /usr/share/perl5/JSON.pm line 190
4. Apply patch
5. Repeat
6. No error

Note: The barclaycard plugin won't install even though it is returned as of this note - the plugin needs an update I believe, I don't think it's a Koha issue
Signed-off-by: David Nind <david@davidnind.com>
JD amended patch: fix indentation

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>