Fix build from sources error

[themarpe]

• Properly logs when building from Source Code (no submodules) downloaded package from GitHub
• Fixes when proper core (with submodules) package is extracted and used under an existing parent git repo

Both are improvements for initial Getting Started UX

[themarpe]

A possible TODO is adding a CI check for these cases:

• Using the proper package, extract & build (should succeed)
• Using the proper package under an existing parent git repo, extract & build (should succeed)
• Using "Source Code" package, extract & build (should fail, with specific error message)
• Cloning without submodules initialized, extract & build (should fail, with specific error message)