Vulkan: Fix infinite loop in state_rebuilder.
Vulkan: Fix infinite loop in state_rebuilder.

The problematic case is a state containing multiple pipelines, some of which
have 0 basePipeline, and some of which have a basePipeline that forms a loop or
doesn't exist. This caused both `numHandled` and `len(unhandledPipelines)` to be
non-zero forever. This change resets `numHandled` for each pass over
`unhandledPipelines`.

Fixes #2390

google/gapid,Qining/gapid,Qining/gapid,pmuetschard/gapid,pmuetschard/gapid,Qining/gapid,google/gapid,pmuetschard/gapid,google/agi,google/agi,Qining/gapid,google/gapid,google/gapid,pmuetschard/gapid,google/agi,Qining/gapid,google/gapid,google/agi,google/gapid,google/agi,google/agi,google/gapid,Qining/gapid,pmuetschard/gapid,Qining/gapid,pmuetschard/gapid,google/agi,pmuetschard/gapid,pmuetschard/gapid,Qining/gapid,google/agi,google/gapid