Magnification isn't reset when service is disabled

If the disabled service is the last service to magnify, reset the
magnification.

Bug: 28623059
Test: manual
Test: atest CtsAccessibilityTestCases
Test: atest CtsAccessibilityServiceTestCases
Test: testResetIfNeeded_resetsOnlyIfLastMagnifyingServiceIsDisabled
Change-Id: I6b12a5251b5fede8d2c9eb06048bf9fa4bd70f8b
4 files changed