Bump up PassCmd buffer size to 2KiB

While ordinary passwords are rarely longer than 80 bytes, XOAUTH2 tokens
easily exceed this limit. Let's bump it up to 2K to be really safe.

src/drv_imap.c

@@ -1875,7 +1875,7 @@ ensure_password( imap_server_conf_t *srvc )
 	if (cmd) {
 		FILE *fp;
 		int ret;
-		char buffer[80];
+		char buffer[2048];  // Hopefully more than enough room for XOAUTH2, etc. tokens
 
 		if (*cmd == '+') {
 			flushn();