failback to Content-Type filename when encoded Content-Disposition is used

Hi!
This patch will fix missing filename if it is RFC2231 encoded with charset
different then ASCII or UTF8. Example how it looks like in mail:

Content-Type: application/pdf;
 name="=?UTF-8?Q?Opis_przedmiotu_zam=c3=b3wienia_-_za=c5=82=c4=85cznik_nr_1?=
 =?UTF-8?Q?=2epdf?="
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename*0*=iso-8859-2''%4F%70%69%73%20%70%72%7A%65%64%6D%69%6F%74%75%20;
 filename*1*=%7A%61%6D%F3%77%69%65%6E%69%61%20%2D%20%7A%61%B3%B1%63%7A%6E;
 filename*2*=%69%6B%20%6E%72%20%31%2E%70%64%66

Yes, this should be forbidden :-). Anyway, best solotion in such cases
is to failback to Content-Type name. I am not sure if it is guaranted to
be there, but probably it will.

Leszek

commands/msgview/save.go

@@ -94,6 +94,8 @@ func (Save) Execute(aerc *widgets.Aerc, args []string) error {
 			save_dir = path
 			if filename, ok := p.Part.DispositionParams["filename"]; ok {
 				save_file = filename
+			} else if filename, ok := p.Part.Params["name"]; ok {
+				save_file = filename
 			} else {
 				timestamp := time.Now().Format("2006-01-02-150405")
 				save_file = fmt.Sprintf("aerc_%v", timestamp)