[BUG] Extension variations shown as possible update target

[liayn]

If an extension is used in a modified way at one of the clients with a higher version number than officially available, the version is advertised as update for all other clients as well.
The version is marked as non-official correctly in DB, hence it shouldn't be suggested as update target.

Example: realurl official version latest version is 2.0.14. Latest version from git is 2.1.0. Having 2.1.0 installed at one client will show the 2.1.0 version also for all other clients.