Skip headless user when reset all IME users

Command `adb shell ime reset --user all` crashes with NPE when running
on HSUM surfaces. This fix will prevent IMMS to list IMEs for headless
users.

Fix: 295476022
Test: manual (ran `adb shell ime reset --user all`)
Test: atest CtsInputMethodTestCases
Change-Id: I22b71ff0482cf18c10716b52504c95ffb991796f
1 file changed