Make sure default values are used when project data is unavailable

What does this MR do and why?

Following the pattern from ee/app/assets/javascripts/repository/components/header_area/blob_overflow_menu.vue, this MR makes sure that optional chaining operator and default values are used for pathLocks and userPermission in the BlobContentViewer.

References

• Fix TypeError regarding pathLocks in blob_content_viewer
• example error

Screenshots or screen recordings

Before	After
n/a	n/a

How to set up and validate locally

1. Go to Project / Repository and select a file to view
2. Inspect BlobContentViewer with the Vue devTools
3. Apply the following patch and make sure that devTools show values from BLOB_DEFAULT_INFO

diff --git a/app/assets/javascripts/repository/components/blob_content_viewer.vue b/app/assets/javascripts/repository/components/blob_content_viewer.vue
index 4f35064d837e..66fb8b6ef493 100644
--- a/app/assets/javascripts/repository/components/blob_content_viewer.vue
+++ b/app/assets/javascripts/repository/components/blob_content_viewer.vue
@@ -72,8 +72,9 @@ export default {
         this.displayError();
       },
       update({ project }) {
-        this.pathLocks = project?.pathLocks || DEFAULT_BLOB_INFO.pathLocks;
-        this.userPermissions = project?.userPermissions || DEFAULT_BLOB_INFO.userPermissions;
+        let prj = {}
+        this.pathLocks = prj?.pathLocks || DEFAULT_BLOB_INFO.pathLocks;
+        this.userPermissions = prj?.userPermissions || DEFAULT_BLOB_INFO.userPermissions;
       },
     },
     project: {

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Related to #523410 (closed)