tray: Work around Electron segfault on certain platforms.
tray: Work around Electron segfault on certain platforms.

Set the tray icon’s context menu immediately after creating the Tray
object.  This seems to prevent an Electron segfault at startup on
certain platforms, such as Ubuntu 16.04 i386.  See
https://github.com/electron/electron/issues/22652 and its linked
issues.

Signed-off-by: Anders Kaseorg <dfdb7392591db597bc41cf266a9c3bc12a2706e5@zulipchat.com>

zulip/zulip-desktop,zulip/zulip-desktop,zulip/zulip-desktop,zulip/zulip-desktop