-Wstrict-bool warning fixes

src/doveadm/doveadm-auth-server.c

@@ -91,7 +91,7 @@ cmd_user_input(struct auth_master_connection *conn,
 		string_t *json_field = t_str_new(show_field_len+1);
 		json_append_escaped(json_field, show_field);
 		o_stream_nsend_str(doveadm_print_ostream, t_strdup_printf("\"%s\":", str_c(json_field)));
-		for (; *fields; fields++) {
+		for (; *fields != NULL; fields++) {
 			if (strncmp(*fields, show_field, show_field_len) == 0 &&
 			    (*fields)[show_field_len] == '=') {
 				string_t *jsonval = t_str_new(32);
@@ -113,7 +113,7 @@ cmd_user_input(struct auth_master_connection *conn,
 			o_stream_nsend_str(doveadm_print_ostream, str_c(jsonval));
 			o_stream_nsend_str(doveadm_print_ostream, "\"");
 		}
-		for (; *fields; fields++) {
+		for (; *fields != NULL; fields++) {
 			const char *field = *fields;
 			if (*field == '\0') continue;
 			p = strchr(*fields, '=');

src/doveadm/doveadm-dump-dcrypt-file.c

@@ -41,7 +41,7 @@ static void dcrypt_istream_dump_metadata(const struct istream *stream)
 	}
 }
 
-static int dcrypt_file_dump_metadata(const char *filename, bool print)
+static bool dcrypt_file_dump_metadata(const char *filename, bool print)
 {
 	bool ret = FALSE;
 	struct istream *is = i_stream_create_file(filename, IO_BLOCK_SIZE);

src/lib-ssl-iostream/iostream-openssl-context.c

@@ -157,7 +157,7 @@ ssl_iostream_ctx_use_dh(struct ssl_iostream_context *ctx,
 
 	if (openssl_iostream_load_dh(set, &dh, error_r) < 0)
 		return -1;
-	if (!SSL_CTX_set_tmp_dh(ctx->ssl_ctx, dh)) {
+	if (SSL_CTX_set_tmp_dh(ctx->ssl_ctx, dh) == 0) {
 		 *error_r = t_strdup_printf(
 			"Can't load DH parameters: %s",
 			openssl_iostream_key_load_error());