ggml-vulkan: don't assert compute_ctx empty before perf timestamp

Pinned async host uploads can record into compute_ctx before graph
compute, so the perf logger's opening timestamp must append after them
instead of asserting the context is expired. Without this, profiling
(GGML_VK_PERF_LOGGER) crashes whenever host-register pinning is on.

Assisted-by: Claude

ggml/src/ggml-vulkan/ggml-vulkan.cpp

@@ -16685,7 +16685,7 @@ static ggml_status ggml_backend_vk_graph_compute(ggml_backend_t backend, ggml_cg
         std::fill(ctx->query_nodes.begin(), ctx->query_nodes.end(), nullptr);
         std::fill(ctx->query_node_idx.begin(), ctx->query_node_idx.end(), 0);
 
-        GGML_ASSERT(ctx->compute_ctx.expired());
+        // compute_ctx may hold async host uploads recorded before the graph; append the timestamp after them
         compute_ctx = ggml_vk_get_compute_ctx(ctx);
         ctx->query_idx = 0;
         compute_ctx->s->buffer->buf.writeTimestamp(vk::PipelineStageFlagBits::eAllCommands, ctx->query_pool, ctx->query_idx++);