Sets the default PIDSourceParameter to be kDistance so there is no null pointer exception

Change-Id: Ice4889ea3f6fd5afe6984f9715758a178222837f

wpilibj/wpilibJava/src/main/java/edu/wpi/first/wpilibj/Encoder.java

@@ -99,6 +99,7 @@ public class Encoder extends SensorBase implements CounterBase, PIDSource,
 			break;
 		}
 		m_distancePerPulse = 1.0;
+		m_pidSource = PIDSourceParameter.kDistance;
 
 		UsageReporting.report(tResourceType.kResourceType_Encoder,
 				m_index, m_encodingType.value);