iOS: Enable autorotate on startup.

The qobject_cast to QGuiAppplication will always
fail at startup since QGuiApplication is not ready
yet.

Return YES in that case. Allowed orientations can then
be controlled by setting "Supported Interface Orientations"
in Xcode or the Info.plist file.

Change-Id: Ifd86bbcedabc716e63563bbb7cb0c1c6833fd6c7
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>