Exclude empty dictionaries from bundles to operate on

When Running PluginInstall or PluginUpdate with a list of plugins and
some of those have failed name validation, they are returned as empty
dictionaries. Exclude those before checking the size of the list so that
if all given plugin names failed, then the empty list message is shown.

autoload/vundle/installer.vim

@@ -18,6 +18,8 @@ func! vundle#installer#new(bang, ...) abort
     let bundles = map(copy(a:000), 'vundle#config#bundle(v:val, {})')
   endif
 
+  let bundles = filter(copy(bundles), '!empty(v:val)')
+
   if empty(bundles)
     echoerr 'No bundles were selected for operation'
     return