Improve guard to support concatenated files

autoload/julia_latex_symbols.vim

@@ -1,7 +1,4 @@
-if exists('g:polyglot_disabled') && index(g:polyglot_disabled, 'julia') != -1
-  finish
-endif
-
+if !exists('g:polyglot_disabled') || index(g:polyglot_disabled, 'julia') == -1
 " This file is autogenerated from the script 'generate_latex_symbols_table.jl'
 " The symbols are based on Julia version 1.3.0-DEV.263
 
@@ -3332,3 +3329,4 @@ function! julia_latex_symbols#get_dict()
     \ '\:baggage_claim:': '🛄',
     \ '\:left_luggage:': '🛅'}
 endfunction
+endif