Eliminate potential NPEs with ChangeData.getChange()

Callers were supposed to be calling hasChange() to determine whether
getChange() would return null, but none were. Remove this error-prone
pair of methods and just use change(), which includes lazy loading.
There are a few places where we need to catch an additional
OrmException but these are easy enough to fix.

Change-Id: I23335e362715f59e2c093ffec88427739ff0cffc

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

@@ -384,7 +384,7 @@ public class ChangeJson {
     }
 
     LabelTypes labelTypes = ctl.getLabelTypes();
-    if (cd.getChange().getStatus().isOpen()) {
+    if (cd.change().getStatus().isOpen()) {
       return labelsForOpenChange(cd, labelTypes, standard, detailed);
     } else {
       return labelsForClosedChange(cd, labelTypes, standard, detailed);