merge pull request from athaeryn

Closes #19.

autoload/startify.vim

@@ -36,6 +36,9 @@ function! startify#delete_session(...) abort
   if !isdirectory(g:startify_session_dir)
     echo 'The session directory does not exist: '. g:startify_session_dir
     return
+  elseif empty(startify#get_session_names_as_string(''))
+    echo 'There are no sessions...'
+    return
   endif
   let spath = g:startify_session_dir . startify#get_separator() . (exists('a:1')
         \ ? a:1
@@ -88,6 +91,9 @@ function! startify#load_session(...) abort
   if !isdirectory(g:startify_session_dir)
     echo 'The session directory does not exist: '. g:startify_session_dir
     return
+  elseif empty(startify#get_session_names_as_string(''))
+    echo 'There are no sessions...'
+    return
   endif
   let spath = g:startify_session_dir . startify#get_separator() . (exists('a:1')
         \ ? a:1