Fix MRD patch request with overwriting metrics

Follow-up for [1]
Patch request with body:

{"Metrics": [{"MetricProperties": ["<path_to_sensor>"]}]}

updates metric properly, without appending to old "MetricProperties"
values

[1]: https://gerrit.openbmc.org/c/openbmc/bmcweb/+/76532

Change-Id: I9e2bbea28f3b17adeb61c7f3e54eec87c103ef54
Signed-off-by: Boleslaw Ogonczyk Makowski <boleslawx.ogonczyk-makowski@intel.com>
diff --git a/redfish-core/lib/metric_report_definition.hpp b/redfish-core/lib/metric_report_definition.hpp
index 5006936..91a2b57 100644
--- a/redfish-core/lib/metric_report_definition.hpp
+++ b/redfish-core/lib/metric_report_definition.hpp
@@ -1244,7 +1244,10 @@
                     const ReadingParameters::value_type& existing =
                         readingParams[index];
 
-                    pathAndUri = std::get<0>(existing);
+                    if (metric->empty())
+                    {
+                        pathAndUri = std::get<0>(existing);
+                    }
                     metricArgs.collectionFunction = std::get<1>(existing);
                     metricArgs.collectionTimeScope = std::get<2>(existing);
                     metricArgs.collectionDuration = std::get<3>(existing);