Include the possibility of combining four objects

Simply add `&& lists != 4` in:
```
if (lists != 2 && lists != 3)
```

Author: Ma128-bit

CommonTools/CandAlgos/interface/CandCombiner.h

@@ -81,7 +81,7 @@ namespace reco {
           throw edm::Exception(edm::errors::Configuration, "failed to parse \"" + decay + "\"");
 
         int lists = labels_.size();
-        if (lists != 2 && lists != 3)
+        if (lists != 2 && lists != 3 && lists != 4)
           throw edm::Exception(edm::errors::LogicError, "invalid number of collections");
         bool found;
         const string setLongLived("setLongLived");