Fix crash coming from accessing invalid display from GestureDetector

- Quick removal of display during boot-up leads into system server crash
- Check if display is still existing before creating GestureDetector

Bug: 157256737
Test: N/A (need to check occasional failures in emulator tests)
Change-Id: I2b04b0e8dea195ffdb1ac1390ef2ba0d4eebfd1b