Prevent raw contact picker dialog from flashing

If the dialog is currently shown and the loader calls onLoadFinished
again, update the cursor without doing another fragment transaction.

Test:
Followed repro steps in bug, confirming that the dialog doesn't
flash in and out, along with debug log statements to confirm
it goes through the setCursor call.

Bug: 32096586
Change-Id: Ia021c66e65adb6b4e34b0d4e3a0e521a31e3086f