fix(core): handle nullable lock when creating project graph (#30000)

## Current Behavior

The project graph construction can throw an error when the lock is not
created:
#29821 (comment).

## Expected Behavior

The project graph construction should correctly handle the nullable
lock.

## Related Issue(s)

Fixes #

packages/nx/src/project-graph/project-graph.ts

@@ -363,7 +363,7 @@ export async function createProjectGraphAndSourceMapsAsync(
     } catch (e) {
       handleProjectGraphError(opts, e);
     } finally {
-      lock.unlock();
+      lock?.unlock();
     }
   } else {
     try {