Avoid NPE when retrieving null relationsDepth (#288)

The NPE leads to a broken cache inside of weborb's serializer - it merely can't see that there's a relationsDepth field and ignores it further.

Author: scadgek

src/com/backendless/persistence/QueryOptions.java

@@ -99,7 +99,7 @@ public void setRelationsDepth ( Integer relationsDepth )
     this.relationsDepth = relationsDepth;
   }
 
-  public int getRelationsDepth()
+  public Integer getRelationsDepth()
   {
     return relationsDepth;
   }