CloudMonitoring: Prevent resource type variable function from crashing (#30901)

* check if label response has resource type prop

* use nullish coalescing operator

public/app/plugins/datasource/cloud-monitoring/CloudMonitoringMetricFindQuery.ts

@@ -112,7 +112,7 @@ export default class CloudMonitoringMetricFindQuery {
     }
     const refId = 'handleResourceTypeQueryQueryType';
     const labels = await this.datasource.getLabels(selectedMetricType, refId, projectName);
-    return labels['resource.type'].map(this.toFindQueryResult);
+    return labels['resource.type']?.map(this.toFindQueryResult) ?? [];
   }
 
   async handleAlignersQuery({ selectedMetricType, projectName }: CloudMonitoringVariableQuery) {

public/app/plugins/datasource/cloud-monitoring/components/VariableQueryEditor.tsx

@@ -150,7 +150,7 @@ export class CloudMonitoringVariableQueryEditor extends PureComponent<Props, Var
       selectedMetricType,
       ...(await this.getLabels(selectedMetricType, this.state.projectName)),
     };
-    this.setState(state);
+    this.setState(state, () => this.onPropsChange());
   }
 
   async onMetricTypeChange(metricType: string) {
@@ -158,7 +158,7 @@ export class CloudMonitoringVariableQueryEditor extends PureComponent<Props, Var
       selectedMetricType: metricType,
       ...(await this.getLabels(metricType, this.state.projectName)),
     };
-    this.setState(state);
+    this.setState(state, () => this.onPropsChange());
   }
 
   onLabelKeyChange(labelKey: string) {