bootstrap.js: restructure for readability

Now we require one less level of indentation. As a consequence, this
commit is easier to read with Git's -w option (ignoring whitespace
changes).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
bootstrap.js: try harder to show the GUI

Even if ImageJ 1.x is not initialized, the user probably wants to see
some window.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>