Fix a bug in completion metrics

I found this while testing a change to the computation of the completion
location in `OpType`. The experiment started producing a completion
location that wasn't previously produced, and that's what led to it being
a key for one set of data but not in the other set of data.

Change-Id: I3938ae68ec61afbef98d9674c7d6377fa4120d4a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/211100
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Brian Wilkerson <[email protected]>

Author: bwilkerson

pkg/analysis_server/tool/code_completion/completion_metrics.dart

@@ -1071,8 +1071,9 @@ class CompletionMetricsComputer {
           .toList();
       locations.sort();
       for (var location in locations) {
-        table.add(toRow(targetMetrics
-            .map((metrics) => metrics.locationMrrComputers[location]!)));
+        table.add(toRow(targetMetrics.map((metrics) =>
+            metrics.locationMrrComputers[location] ??
+            MeanReciprocalRankComputer(location))));
       }
     }
     rightJustifyColumns(table, range(1, table[0].length));