Fixed bug causing user to be stuck on face intro

Test: See below
Fixes: 203375738
Change-Id: I3e59191a8c936c7c7a3d8561e908593dbf9710b5

1. Enrolled a face during SUW
2. Pressed back on fingerprint enroll intro
3. Verified that the next button's text is chnaged to done
4. The done action launches the fingerprint enroll intro flow.

Change-Id: Id5d652257445e40426ade3d396a31ebf936cc348

src/com/android/settings/biometrics/BiometricEnrollIntroduction.java

@@ -257,8 +257,12 @@ public abstract class BiometricEnrollIntroduction extends BiometricEnrollBase
             // Lock thingy is already set up, launch directly to the next page
             launchNextEnrollingActivity(mToken);
         } else {
-            setResult(RESULT_FINISHED);
-            finish();
+            boolean couldStartNextBiometric = BiometricUtils.tryStartingNextBiometricEnroll(this,
+                    ENROLL_NEXT_BIOMETRIC_REQUEST, "enrollIntroduction#onNextButtonClicked");
+            if (!couldStartNextBiometric) {
+                setResult(RESULT_FINISHED);
+                finish();
+            }
         }
     }