MXS-2266: Close prepared statements with internal ID

The ID used to store the prepared statements uses the internal ID and
using the external ID caused unwanted memory use and a false warning.

server/core/queryclassifier.cc

@@ -390,8 +390,18 @@ uint32_t QueryClassifier::ps_get_type(std::string id) const
 
 void QueryClassifier::ps_erase(GWBUF* buffer)
 {
-    m_ps_handles.erase(qc_mysql_extract_ps_id(buffer));
+    if (qc_mysql_is_ps_command(mxs_mysql_get_command(buffer)))
-    m_sPs_manager->erase(buffer);
+    {
+        // Erase the type of the statement stored with the internal ID
+        m_sPs_manager->erase(ps_id_internal_get(buffer));
+        // ... and then erase the external to internal ID mapping
+        m_ps_handles.erase(qc_mysql_extract_ps_id(buffer));
+    }
+    else
+    {
+        // Not a PS command, we don't need the ID mapping
+        m_sPs_manager->erase(buffer);
+    }
 }
 
 bool QueryClassifier::query_type_is_read_only(uint32_t qtype) const

server/modules/routing/readwritesplit/rwsplit_route_stmt.cc

@@ -451,6 +451,7 @@ bool RWSplitSession::route_session_write(GWBUF* querybuf, uint8_t command, uint3
     }
     else if (qc_query_is_type(type, QUERY_TYPE_DEALLOC_PREPARE))
     {
+        mxb_assert(!mxs_mysql_is_ps_command(m_qc.current_route_info().command()));
         m_qc.ps_erase(querybuf);
     }