Make sure we have a ";" after locale in User Agent

When in pre-release mode, we did not have a semi-colon between
the locale (i.e. "en-us") and the the Build (i.e. "Build/HRH50")

In release mode we correctly added the semi-colon (and put in
the "model") so this was only an issue when in pre-release mode.

Bug: 3215465
Change-Id: Ied1acc69463ffddabbc886e7e7e5e8cc8ab14956