DutyCycleEncoder does not indicate when disconnected.

[fovea1959]

Title says it all.

I think this is the correct patch (untested):

diff --git "a/swervelib/encoders/PWMDutyCycleEncoderSwerve.java" "b/swervelib/encoders/PWMDutyCycleEncoderSwerve.java"
index 5227095..f51ac33 100644
--- "a/swervelib/encoders/PWMDutyCycleEncoderSwerve.java"
+++ "b/swervelib/encoders/PWMDutyCycleEncoderSwerve.java"
@@ -66,6 +66,7 @@ public class PWMDutyCycleEncoderSwerve extends SwerveAbsoluteEncoder
   @Override
   public double getAbsolutePosition()
   {
+    readingError = ! encoder.isConnected();
     return (isInverted ? -1.0 : 1.0) * ((encoder.get() * 360) - offset);
   }