mtmd: use causal attn for gemma 4 audio (#21824)

tools/mtmd/mtmd-helper.cpp

@@ -274,7 +274,8 @@ int32_t mtmd_helper_decode_image_chunk(
         batch_embd.set_position_normal(n_past, seq_id);
     }
 
-    if (mtmd_decode_use_non_causal(ctx)) {
+    const bool use_non_causal = mtmd_decode_use_non_causal(ctx, chunk);
+    if (use_non_causal) {
         llama_set_causal_attn(lctx, false);
         // TODO @ngxson : need to make sure only one image is processed at a time, and n_ubatch must be enough to hold the image
     }
@@ -302,7 +303,7 @@ int32_t mtmd_helper_decode_image_chunk(
     n_past += mtmd_input_chunk_get_n_pos(chunk);
     *new_n_past = n_past;
 
-    if (mtmd_decode_use_non_causal(ctx)) {
+    if (use_non_causal) {
         llama_set_causal_attn(lctx, true);
     }
     return 0;