[v0.18.0][Bugfix] Fix the bug of MTP1 crashing in multiple concurrent scenarios. (#7699)

### What this PR does / why we need it?
The triton operator does not perform boundary checks on the global
position within the loop, leading to the memory overflow in scenarios
with multiple concurrency + 1-step MTP launch.

Solution: Add a check that global_pos < vec_len, and strictly limit the
boundaries of all memory accesses to avoid out-of-bounds writes.
backport：#7459

Signed-off-by: Bowen-Leee <caoshankuangren@gmail.com>

vllm_ascend/ops/triton/reject_sample.py

@@ -58,16 +58,19 @@ def rejection_greedy_sample_spec_len_1_triton(
     target_argmax_id = tl.load(target_argmax_ptr + offset, mask)
     tl.store(output_token_ids_ptr + offset * 2, target_argmax_id, mask)
 
+    # Add validity check for pos within the loop
     for pos in tl.range(0, BLOCK_SIZE):
-        draft_token_id1 = get_element(draft_token_id, (pos,))
-        target_argmax1 = get_element(target_argmax_id, (pos,))
-        position = block_idx * BLOCK_SIZE + pos
-        if draft_token_id1 == target_argmax1:
-            bonus_renew_1(
-                bonus_token_ids_ptr,
-                position,
-                output_token_ids_ptr,
-            )
+        # Calculate the global position of the current token
+        global_pos = block_idx * BLOCK_SIZE + pos
+        if global_pos < vec_len:
+            draft_token_id1 = get_element(draft_token_id, (pos,))
+            target_argmax1 = get_element(target_argmax_id, (pos,))
+            if draft_token_id1 == target_argmax1:
+                bonus_renew_1(
+                    bonus_token_ids_ptr,
+                    global_pos,
+                    output_token_ids_ptr,
+                )
 
 
 @triton.jit(do_not_specialize=["max_spec_len"])