Fixing some NPEs related to having an empty leaderboard.

src/main/java/com/gmail/nossr50/util/Leaderboard.java

@@ -48,6 +48,7 @@ public class Leaderboard {
 
             while ((line = in.readLine()) != null) {
                 String[] character = line.split(":");
+
                 String p = character[0];
                 int powerLevel = 0;
 
@@ -126,6 +127,9 @@ public class Leaderboard {
             plugin.getLogger().severe(("Exception while reading " + location + " (Are you sure you formatted it correctly?)" + e.toString()));
         }
 
+        if(PowerLevel.isEmpty())
+            return;
+
         //Sort the leader boards
         SkillComparator c = new SkillComparator();
         Collections.sort(Mining, c);