nir/opt_remove_phis: handle phis with no sources
This can happen with loops with unreachable exits which are later optimized away.
Fixes assertion in dEQP-VK.graphicsfuzz.unreachable-loops with RADV.
Edited by Rhys Perry
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This can happen with loops with unreachable exits which are later optimized away.
Fixes assertion in dEQP-VK.graphicsfuzz.unreachable-loops with RADV.