Job not found

- Gogs version (or commit ref): 0.12.0+dev
- Jenkins version: 2.222.3
- gogs-webhook-plugin version: 1.10.15
- Jenkins modules used in combination with gogs-webhook-plugin: none
- JSON Output of webhook:
- Request:
```
Request URL: https://(server)/gogs-webhook/?job=thejob
Request method: POST
Content-Type: application/json
X-Github-Delivery: 2650ce88-b70f-4425-8e8c-ec79bcbfe6af
X-Github-Event: push
X-Gogs-Delivery: 2650ce88-b70f-4425-8e8c-ec79bcbfe6af
X-Gogs-Event: push
X-Gogs-Signature:
```
- Response
```
Content-Length: 69
Content-Type: application/json
Date: Wed, 20 May 2020 13:46:54 GMT
Server: Jetty(9.4.27.v20200227)
X-Content-Type-Options: nosniff

{"result":"ERROR","message":"Job 'thejob' is not defined in Jenkins"}
```

## Description

This seems similar to my original issue in #8, but more recently #36 as I first had the issue with the job in a folder (thefolder/thejob), so I recreated it at root, without a folder, and it is listed with the standard Jenkins API. It may be related to #22 as this is a multibranch pipeline.
```
(server)/api/json?tree=jobs[name,builds[number,actions[parameters[name,value]]]]&pretty=true

"_class": "hudson.model.Hudson",
"jobs": [
{
"_class": "com.cloudbees.hudson.plugins.folder.Folder",
"name": "thefolder"
},
{
"_class": "org.jenkinsci.plugins.workflow.multibranch.WorkflowMultiBranchProject",
"name": "thejob"
}
{
"_class": "hudson.model.FreeStyleProject",
"name": "test",
"builds": [

]
}
]
}
```

Branch discovery works normally in the Jenkins UI. When I use the same format to test a non-multibranch job (the `test` job), it works normally, hence the link to #22. Such normal jobs also work in folders (calling `?job=thefolder/test`)

Same error when trying the hook on `?job=thejob/master`, although it works with other branches beyond master, as described near the end of #8.