fix LOGIN in SASL builds

if AuthMechs includes more than just LOGIN and the server announces any
AUTH= mechanism, we try SASL. but that can still fail to find any
suitable authentication mechanism, and we must not error out in that
case if we are supposed to fall back to LOGIN.

src/drv_imap.c

@@ -1992,6 +1992,8 @@ imap_open_store_authenticate2( imap_store_t *ctx )
 
 		rc = sasl_client_new( "imap", srvc->sconf.host, NULL, NULL, NULL, 0, &ctx->sasl );
 		if (rc != SASL_OK) {
+			if (rc == SASL_NOMECH)
+				goto notsasl;
 			if (!ctx->sasl)
 				goto saslbail;
 			error( "Error: %s\n", sasl_errdetail( ctx->sasl ) );
@@ -1999,6 +2001,8 @@ imap_open_store_authenticate2( imap_store_t *ctx )
 		}
 
 		rc = sasl_client_start( ctx->sasl, saslmechs + 1, &interact, CAP(SASLIR) ? &out : NULL, &out_len, &gotmech );
+		if (rc == SASL_NOMECH)
+			goto notsasl;
 		if (gotmech)
 			info( "Authenticating with SASL mechanism %s...\n", gotmech );
 		/* Technically, we are supposed to loop over sasl_client_start(),
@@ -2017,6 +2021,8 @@ imap_open_store_authenticate2( imap_store_t *ctx )
 		imap_exec( ctx, cmd, done_sasl_auth, enc ? "AUTHENTICATE %s %s" : "AUTHENTICATE %s", gotmech, enc );
 		free( enc );
 		return;
+	  notsasl:
+		sasl_dispose( &ctx->sasl );
 	}
 #endif
 	if (auth_login) {