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

(cherry picked from commit e0d64a13)

Change-Id: I7306b3113ca14ed92dd1740c0d682c1e51c1e52a