This is a follow-up of https://github.com/nativefier/nativefier/pull/1162#discussion_r623766247
PR #1162 introduced a new `generateRandomSuffix` helper function,
used it for its needs (avoiding collisions of injected js/css).
But it also replaced existing appname normalizing logic with it,
introducing randomness in a place that used to be deterministic.
As a result, starting with dd6e15fb5 / v43.1.0, re-creating an app would cause
the app to use a different appName, thus a different appData folder, thus
losing user data including cookies.
This PR leaves the `--inject` fixes of #1176, but reverts the appName logic
to the pre-#1176 code.