context: Only call JS_SetCStringsAreUTF8() once
context: Only call JS_SetCStringsAreUTF8() once

The JS engine mandates that this is called once, and before
the first runtime is constructed. This is enforced by an
assertion that's turned on in debug builds.

https://bugzilla.gnome.org/show_bug.cgi?id=691108

pixunil/cjs,djdeath/gjs,pixunil/cjs,pixunil/cjs,mtwebster/cjs,djdeath/gjs,pixunil/cjs,mtwebster/cjs,endlessm/gjs,djdeath/gjs,endlessm/gjs,djdeath/gjs,djdeath/gjs,endlessm/gjs,mtwebster/cjs,mtwebster/cjs,endlessm/gjs,endlessm/gjs,mtwebster/cjs,pixunil/cjs