Extra check on getLastPlayed

In case getOfflinePlayer failed, or getting a proper claim owner failed
somehow.

Yup, that's where I was going to add it.
Closes #22

src/me/ryanhamshire/GriefPrevention/CleanupUnusedClaimPreTask.java

@@ -43,6 +43,7 @@ class CleanupUnusedClaimPreTask implements Runnable
 	    //expiration code uses last logout timestamp to decide whether to expire claims
 	    //don't expire claims for online players
 	    if(ownerInfo.isOnline()) return;
+		if(ownerInfo.getLastPlayed() <= 0) return;
 	    
 	    GriefPrevention.AddLogEntry("Looking for expired claims.  Checking data for " + claim.ownerID.toString(), CustomLogEntryTypes.Debug, true);