test-case: latency-metrics: fix no metrics JSON

Fix output JSON in case there is no metrics gathered
in non-trial mode, e.g. if gawk is missing on the DUT.

Signed-off-by: Dmitrii Golovanov <dmitrii.golovanov@intel.com>

Author: golowanow

test-case/latency-metrics.sh

@@ -235,7 +235,10 @@ report_metric()
     printf '"probes":0, "xruns":0}' >> "${RESULT_JSON}"
     [ -f "${METRICS_JSON}" ] && rm "${METRICS_JSON}"
     [ -f "${EVENTS_JSON}" ] && rm "${EVENTS_JSON}"
-    [ "${trial_mode}" -ne 0 ] || skip_test "No latency metrics collected"
+    if [ "${trial_mode}" -eq 0 ]; then
+      printf ']}' >> "${RESULT_JSON}"
+      skip_test "No latency metrics collected"
+    fi
   else
     local metrics_
     metrics_=$(cat "${METRICS_JSON}")