Improve guard so it works for no eof new line

ftplugin/zig.vim

@@ -1,4 +1,5 @@
 if !exists('g:polyglot_disabled') || index(g:polyglot_disabled, 'zig') == -1
+
 " Only do this when not done yet for this buffer
 if (exists("b:did_ftplugin"))
   finish
@@ -13,4 +14,5 @@ set shiftwidth=4
 setlocal suffixesadd=.zig
 setlocal commentstring=//\ %s
 setlocal makeprg=zig\ build
+
 endif