disable closure

There's now a new warning when closure isn't set explicitly
for non-WASM builds. Currently, there are errors concerning
redeclaration of the variable screen with closure enabled,
so explicitly disable it.
For the future, we probably want to remove the redeclaration
and enable closure.

Cherry-picked from: libass@45a05db

Author: TheOneric

Makefile

@@ -191,6 +191,7 @@ dist/js/subtitles-octopus-worker-legacy.js: src/subtitles-octopus-worker.bc src/
 		-s LEGACY_VM_SUPPORT=1 \
 		-s MIN_CHROME_VERSION=27 \
 		-s MIN_SAFARI_VERSION=60005 \
+		--closure=0 \
 		$(EMCC_COMMON_ARGS)
 
 dist/js/subtitles-octopus.js: dist/license/all src/subtitles-octopus.js