Fix warning about default snippets

Don't ignore runtime_dir, which is added in case
snipmate compatibility is set.

Fixes https://github.com/Shougo/neosnippet.vim/issues/432

autoload/neosnippet/variables.vim

@@ -55,12 +55,7 @@ endfunction
 function! neosnippet#variables#runtime_dir() abort
   " Set runtime dir.
   let runtime_dir = split(globpath(&runtimepath, 'neosnippets'), '\n')
-  if empty(runtime_dir) && empty(g:neosnippet#disable_runtime_snippets)
-    call neosnippet#util#print_error(
-          \ 'neosnippet default snippets cannot be loaded.')
-    call neosnippet#util#print_error(
-          \ 'You must install neosnippet-snippets or disable runtime snippets.')
-  endif
+
   if g:neosnippet#enable_snipmate_compatibility
     " Load snipMate snippet directories.
     let runtime_dir += split(globpath(&runtimepath,
@@ -70,6 +65,13 @@ function! neosnippet#variables#runtime_dir() abort
     endif
   endif
 
+  if empty(runtime_dir) && empty(g:neosnippet#disable_runtime_snippets)
+    call neosnippet#util#print_error(
+          \ 'neosnippet default snippets cannot be loaded.')
+    call neosnippet#util#print_error(
+          \ 'You must install neosnippet-snippets or disable runtime snippets.')
+  endif
+
   return map(runtime_dir, 'substitute(v:val, "[\\\\/]$", "", "")')
 endfunction
 function! neosnippet#variables#data_dir() abort