improve named part/attachment detection

will now detect filenames for parts if the part specifies Content-Disposition without a filename parameter and Content-Type with a name parameter

mshow.c

@@ -158,11 +158,11 @@ mime_filename(struct message *msg)
 	static char buf[512];
 	char *v;
 	char *filename = 0;
-
-	if ((v = blaze822_hdr(msg, "content-disposition"))) {
-		if (blaze822_mime2231_parameter(v, "filename",
-		    buf, sizeof buf, "UTF-8"))
-			filename = buf;
+	
+	if ((v = blaze822_hdr(msg, "content-disposition")) &&
+	    blaze822_mime2231_parameter(v, "filename",
+	    buf, sizeof buf, "UTF-8")) {
+		filename = buf;
 	} else if ((v = blaze822_hdr(msg, "content-type"))) {
 		if (blaze822_mime2231_parameter(v, "name",
 		    buf, sizeof buf, "UTF-8"))