After Camunda restart existing deployments are not registered with the engine

Steps to reproduce:

1. Start Camunda Platform in version 7.12
2. Create a process application containing a BPMN process
3. Deploy that process application -> a process definition in version 1 is created:

   ENGINE-08023 Deployment summary for process archive 'foo':
   
           process.bpmn
   
   06-Apr-2020 15:36:01.944 INFORMATION [Catalina-utility-2] org.camunda.commons.logging.BaseLogger.logInfo ENGINE-07021 ProcessApplication 'foo' registered for DB deployments [1]. Will execute process definitions
   
           process[version: 1, id: proocess:...]
   

4. Adjust the process application by changing the BPMN process
5. Redeploy process application -> a process definition in version 2 is created:

   ENGINE-08023 Deployment summary for process archive 'foo':
   
           process.bpmn
   
   06-Apr-2020 15:40:01.944 INFORMATION [Catalina-utility-2] org.camunda.commons.logging.BaseLogger.logInfo ENGINE-07021 ProcessApplication 'foo' registered for DB deployments [1, 2]. Will execute process definitions
   
           process[version: 1, id: proocess:...]
           process[version: 2, id: proocess:...]
   

6. Open Cockpit and delete the latest process definition (version 2)
7. Restart the server

Expected Behavior:

• The deployment for process definition version is registered with the engine

  ENGINE-08023 Deployment summary for process archive 'foo':
  
          process.bpmn
  
  06-Apr-2020 15:40:01.944 INFORMATION [Catalina-utility-2] org.camunda.commons.logging.BaseLogger.logInfo ENGINE-07021 ProcessApplication 'foo' registered for DB deployments [1, 2]. Will execute process definitions
  
          process[version: 1, id: proocess:...]
  

Observed Behavior:

• The existing deployment for process definition version 1 is not registered with the engine:

  ENGINE-08023 Deployment summary for process archive 'foo':
  
          process.bpmn
  
  04-Apr-2020 17:06:23.569 INFO [main] org.camunda.commons.logging.BaseLogger.logInfo ENGINE-07021 ProcessApplication 'foo' registered for DB deployments [2]. Deployment does not provide any process definitions.Deployment does not provide any case definitions.
  

So that:

• When using embedded forms, these forms cannot be loaded anymore.
• Java classes cannot be found.

Hint:

• With 7.11, the registration happens as expected.
• With 7.11, ignored resources are kept and registered with the engine:
  • https://github.com/camunda/camunda-bpm-platform/blob/7.11.0/engine/src/main/java/org/camunda/bpm/engine/impl/cmd/DeployCmd.java#L136
  • https://github.com/camunda/camunda-bpm-platform/blob/7.11.0/engine/src/main/java/org/camunda/bpm/engine/impl/cmd/DeployCmd.java#L153-L154
• With 7.12, the registration does not happen anymore because the ignored resources are being completely ignored:
  • https://github.com/camunda/camunda-bpm-platform/blob/master/engine/src/main/java/org/camunda/bpm/engine/impl/cmd/DeployCmd.java#L492-L505
  • Especially this line returns nothing because there isn't any existing process definition for the deployment to register: https://github.com/camunda/camunda-bpm-platform/blob/master/engine/src/main/java/org/camunda/bpm/engine/impl/cmd/DeployCmd.java#L496
• When deleting a process definition, the respective byte array is not deleted.