Fix for several error spotted by static analyzer

[ntfshard]

• Check size before memory access -- we can access 1 extra element out of array
• Use logical operator for bool type variables
• Extra break removed

[ntfshard]

Also couple of places which is not clear, may be you could comment it:

• bus/inputcontext.c:2845: The if condition is the same as the previous if condition:

    if (use_extension)
        context->preedit_visible = visible;
    if (use_extension)
        context->preedit_mode = mode;

src/ibusaccelgroup.c:385: len -= len;

[fujiwarat]

Thank you for the patch.
Regarding to "src/ibusaccelgroup.c:385: len -= len;", I copied gtk_accelerator_parse_with_keycode() to ibus so please report the issue to gtk at first:
https://gitlab.gnome.org/GNOME/gtk/-/blob/master/gtk/gtkaccelgroup.c#L475