Fix atlassian API deleting the current version.

It turns out that AttachmentManager.getPreviousVersions can actually return the current version.

I'm looking into finding out what conditions cause this but have for the moment put in protection to stop us deleting the current version.

src/main/java/com/drunkendev/confluence/plugins/attachments/PurgeAttachmentsJob.java

@@ -30,6 +30,7 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import org.apache.commons.lang3.StringUtils;
 import org.apache.commons.lang3.tuple.ImmutablePair;
 import org.quartz.JobExecutionContext;
@@ -43,6 +44,7 @@
 import static java.util.Comparator.nullsFirst;
 import static java.util.stream.Collectors.toList;
 import static java.util.stream.Collectors.toMap;
+import static java.util.stream.Collectors.toSet;
 import static org.apache.commons.lang.StringUtils.isNotBlank;
 import static org.apache.commons.lang3.StringUtils.repeat;
 
@@ -163,7 +165,18 @@ public void doExecute(JobExecutionContext jec) throws JobExecutionException {
                     counters[IDX_PRIOR_VERSIONS] += prior.size();
 
                     List<Attachment> toDelete = findDeletions(prior, settings);
-                    if (!toDelete.isEmpty()) {
+                    Set<Integer> badVersions = toDelete.stream()
+                            .filter(n -> n.getVersion() >= attachment.getVersion())
+                            .map(n -> n.getVersion())
+                            .collect(toSet());
+                    if (badVersions.size() > 0) {
+                        LOG.error("Attachment bas invalid prior versions: {}:{} :- {} ({}) :: {}",
+                                  attachment.getSpaceKey(),
+                                  attachment.getSpace().getName(),
+                                  attachment.getDisplayTitle(),
+                                  attachment.getVersion(),
+                                  badVersions);
+                    } else if (!toDelete.isEmpty()) {
                         boolean canUpdate;
                         if (!settings.isReportOnly() && !systemSettings.isReportOnly()) {
                             canUpdate = systemSettings.getDeleteLimit() == 0 ||