Fixes issue when settings number of tables of 0

app/src/main/java/net/pokeranalytics/android/model/realm/Session.kt

@@ -294,9 +294,11 @@ open class Session : RealmObject(), Savable, RowUpdatable, RowRepresentable, Tim
 	// The number of tables played at the same time
 	var numberOfTables: Int = 1
 		set(value) {
+			if (value > 0) {
 				field = value
 				this.computeStats()
 			}
+		}
 
 	// The hand histories of the session
 	@LinkingObjects("session")