Clean-up vimpager check.

ftdetect/UltiSnips.vim

@@ -1,10 +1,14 @@
 " This has to be called before ftplugins are loaded. Therefore
 " it is here in ftdetect though it maybe shouldn't
-if !exists("vimpager")
-    if has("autocmd")
+
+" This is necessary to prevent errors when using vim as a pager.
+if exists("vimpager")
+    finish
+endif
+
+if has("autocmd")
     augroup UltiSnipsFileType
         au!
         autocmd FileType * call UltiSnips#FileTypeChanged()
     augroup END
-    endif
-endif
+endif