Bug 11730: ensure that C4::Charset loads C4::Context

Bug 11730: ensure that C4::Charset loads C4::Context

C4::Charset::SetMarcUnicodeFlag() fetches system preference
values, so since it invokes routines in C4::Context, it should
load the module.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit b9d2a832db6d2a75d6466a349b769e8285d1f0c8)

Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit acec28bc4c9319da4490eb940ef54d0875c97c48)