Make sure to return false for empty classpath

Previously, the binder call was returning true causing the test to
fail.

Test: adb shell data/nativetest/installd_dexopt_test/installd_dexopt_test
Bug: 118818285
Bug: 118777746
Change-Id: I1a4c3ee4a0e9ed614c15c95f88489b6bf4e66fa5