Use patchinfo from target package for accepted requests

The source project for maintenance release requests gets
deleted in many cases after it is accepted. Therefore we
have to fetch the patchinfo from the target in those cases.
We also should handle the case of a removed source and target
to prevent nil exceptions.

Fixes openSUSE#16030

src/api/app/views/webui/request/_patchinfo_details.html.haml

@@ -1,6 +1,13 @@
 #patchinfo-details
   %h4.my-3 Patches
   - bs_request.bs_request_actions.where(source_package: 'patchinfo').each do |patchinfo|
-    - patchinfo_package = Package.find_by_project_and_name(patchinfo.source_project, patchinfo.source_package)
-    - patchinfo_text = patchinfo_package.source_file('_patchinfo', rev: patchinfo.source_rev || patchinfo_package.rev)
-    = render PatchinfoComponent.new(patchinfo_text, request_changes_path(number: bs_request.number, request_action_id: patchinfo.id))
+    - patchinfo_source_package = Package.find_by_project_and_name(patchinfo.source_project, patchinfo.source_package)
+    - patchinfo_target_package = Package.find_by_project_and_name(patchinfo.target_project, patchinfo.target_package)
+    - if patchinfo_source_package.present?
+      - patchinfo_text = patchinfo_source_package.source_file('_patchinfo', rev: patchinfo.source_rev || patchinfo_package.rev)
+      = render PatchinfoComponent.new(patchinfo_text, request_changes_path(number: bs_request.number, request_action_id: patchinfo.id))
+    - elsif patchinfo.bs_request_action_accept_info.present? && patchinfo_target_package.present?
+      - patchinfo_text = patchinfo_target_package.source_file('_patchinfo', rev: patchinfo.bs_request_action_accept_info.rev)
+      = render PatchinfoComponent.new(patchinfo_text, request_changes_path(number: bs_request.number, request_action_id: patchinfo.id))
+    - else
+      %p The source and target of #{patchinfo.target_project}/#{patchinfo.target_package} does not exist anymore.