ChangeJson: Less eager loading of patch sets

Normal search results do not include the MESSAGES or any REVISION
options, so they should not need to load the current revision from the
PatchSets table (assuming mergeability cache hits). This was just
wasted DB access, accounting for up to 20% of query traffic.

Change-Id: I641d4af1a71391bcd18ded838224d7a3ee3f57d7

gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeJson.java

@@ -264,7 +264,7 @@ public class ChangeJson {
     ChangeData.ensureChangeLoaded(all);
     if (has(ALL_REVISIONS)) {
       ChangeData.ensureAllPatchSetsLoaded(all);
-    } else {
+    } else if (has(CURRENT_REVISION) || has(MESSAGES)) {
       ChangeData.ensureCurrentPatchSetLoaded(all);
     }
     Set<Change.Id> reviewed = Sets.newHashSet();