Early exit if there are no spans affecting display

In TextLine#handleRun(), exit early and shape the text as one whole
if there were spans, but none of them were a subclass of
MetricAffectingSpan or CharacterStyle.

Change-Id: I859c896ddb9c4828bfddf200e913e98262da6ea3
Fixes: 30985144
Test: cts-tradefed run cts-dev --module CtsTextTestCases
Test: adb shell am instrument -w -e package android.text com.android.frameworks.coretests/android.support.test.runner.AndroidJUnitRunner