Fix NPE when device do NOT has FEATURE_PICTURE_IN_PICTURE

Some project may be config FEATURE_PICTURE_IN_PICTURE = false
If device not support PIP, components in PipController won't initialized,
but OverviewProxyService PipController APIs will lead NPE

Solution: Check if device has system PIP feature before calling

Bug: 161118569
Fixes: 167390795
Test: make SystemUI
Test: make ArcSystemUI
Test: lunch aosp_tv_arm-userdebug & make
Test: atest WindowManagerShellTests
Test: atest SystemUITests
Test: adb shell input keyevent 171(KEYCODE_WINDOW)
Test: manual test Pip demo AP
Change-Id: I0ac17901f31623f04ad5e6787be0f4f25e6066c5