TouchExplorer:Fix test issue with resetting the hover enter timer.

The test handler seems to have some kind of issue with cancelling and reposting the hover enter timer.
To fix this, and to make the system more robust generally, the hover event timer will not do anything if there are no
hover events queued.
This fixes the test failure where the hover enter timer was sending a touch exploration gesture event twice
because it was running twice.
Note that if the real-world handler was acting this way the initial fix this flag controls would have never worked in the first
place.

Fix: 327690468
Test: atest FrameworksServicesTests:TouchExplorerTest CtsAccessibilityServiceTestCases:TouchExplorerTest
Change-Id: Ifac5b28048792d9dd0d2173aac8946703fefce97