Fixed user metric computation for Minetest.

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

@@ -123,7 +123,15 @@ public class MinetestLog
         }
         else
         {
-            result = null;
+            matcher = JOIN_PATTERN.matcher(this.message);
+            if (matcher.matches())
+            {
+                result = matcher.group("nickname");
+            }
+            else
+            {
+                result = null;
+            }
         }
 
         //