[ML] Fix issue with AD data points not showing up because missing indices (#110899) (#111190)

Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>

Co-authored-by: Quynh Nguyen <43350163+qn895@users.noreply.github.com>

Author: kibanamachine

x-pack/plugins/ml/public/application/services/anomaly_explorer_charts_service.ts

@@ -590,7 +590,7 @@ export class AnomalyExplorerChartsService {
         return mlResultsService
           .getMetricData(
             Array.isArray(config.datafeedConfig.indices)
-              ? config.datafeedConfig.indices[0]
+              ? config.datafeedConfig.indices.join()
               : config.datafeedConfig.indices,
             entityFields,
             datafeedQuery,
@@ -777,7 +777,7 @@ export class AnomalyExplorerChartsService {
       return mlResultsService
         .getEventDistributionData(
           Array.isArray(config.datafeedConfig.indices)
-            ? config.datafeedConfig.indices[0]
+            ? config.datafeedConfig.indices.join()
             : config.datafeedConfig.indices,
           splitField,
           filterField,