MXS-1713: Fix resultset collection code

The resultset collection was not detected early enough in the code which
caused partial results to be returned to the router.

maxscale-system-test/mxs1713_lots_of_databases.cpp

@@ -0,0 +1,58 @@
+/**
+ * MXS-1713: SchemaRouter unable to process SHOW DATABASES for a lot of schemas
+ *
+ * https://jira.mariadb.org/browse/MXS-1713
+ */
+#include "testconnections.h"
+#include <vector>
+#include <set>
+#include <numeric>
+
+int main(int argc, char** argv)
+{
+    TestConnections test(argc, argv);
+    const int n_db = 2000;
+    std::vector<std::string> db_list;
+
+    for (int i = 0; i < n_db; i++)
+    {
+        db_list.push_back("db" + std::to_string(i));
+    }
+
+    test.tprintf("Create %lu databases...", db_list.size());
+    test.repl->connect();
+    for (auto db : db_list)
+    {
+        execute_query(test.repl->nodes[0], "CREATE DATABASE %s", db.c_str());
+    }
+    test.tprintf("Done!");
+
+    test.tprintf("Opening a connection with each database as the default database...", db_list.size());
+    std::set<std::string> errors;
+
+    for (auto db : db_list)
+    {
+        MYSQL* conn = open_conn_db(test.maxscales->port(), test.maxscales->ip(), db,
+                                   test.maxscales->user_name, test.maxscales->password);
+        if (execute_query_silent(conn, "SELECT 1") ||
+            execute_query_silent(conn, "SHOW DATABASES"))
+        {
+            errors.insert(mysql_error(conn));
+        }
+        mysql_close(conn);
+    }
+    test.tprintf("Done!");
+
+    test.assert(errors.empty(), "None of the queries should fail: %s",
+                std::accumulate(errors.begin(), errors.end(), std::string(),
+                                [](const std::string &a, const std::string &b){return a + b + " ";}));
+
+    test.tprintf("Dropping databases...");
+    for (auto db : db_list)
+    {
+        execute_query(test.repl->nodes[0], "DROP DATABASE %s", db.c_str());
+    }
+    test.tprintf("Done!");
+
+    return test.global_result;
+}