Fixed user metric computation for Minetest.

src/fr/devinsy/statoolinfos/metrics/minetest/MinetestLog.java

@@ -122,9 +122,17 @@ public class MinetestLog
             result = matcher.group("nickname");
         }
         else
+        {
+            matcher = JOIN_PATTERN.matcher(this.message);
+            if (matcher.matches())
+            {
+                result = matcher.group("nickname");
+            }
+            else
             {
                 result = null;
             }
+        }
 
         //
         return result;