guest-pin-stream: skip non-readable VMAs in the high-VA scan

A CUDA device buffer is a PROT_NONE reservation (often hundreds of MB).
Its pages are never present in the pagemap, so scanning it yields no
pairs - but it consumed the VMA_MAX_PAGES budget, and the scan never
reached the client's present staging buffers that sit ABOVE the device
reservation. Observed: a client whose device range started below its
staging buffer got no high-VA pins at all; its H2D copies failed rc=-2
forever and the client read back stale data (soak run: 9/9 green then
streams2 bad=32737). Skipping '---' VMAs restores the pins (9 fresh
high-VA injections in the first run; streams2 bad=0).

0 files changed, 0 insertions, 0 deletions