fix flatten pack1to4

src/layer/flatten.cpp

@@ -138,7 +138,7 @@ int Flatten::forward(const VkMat& bottom_blob, VkMat& top_blob, VkCompute& cmd,
     constants[3].i = bottom_blob.c;
     constants[4].i = bottom_blob.cstep;
     constants[5].i = top_blob.dims;
-    constants[6].i = (packing == 1 && out_packing == 4) ? top_blob.w * out_packing : top_blob.w;
+    constants[6].i = (packing == 1 && out_packing == 4) ? total : top_blob.w;
     constants[7].i = top_blob.h;
     constants[8].i = top_blob.c;
     constants[9].i = top_blob.cstep;
@@ -148,7 +148,18 @@ int Flatten::forward(const VkMat& bottom_blob, VkMat& top_blob, VkCompute& cmd,
     // record
     cmd.record_prepare_compute_barrier(bottom_blob);
     cmd.record_prepare_compute_barrier(top_blob);
-    cmd.record_pipeline(pipeline, bindings, constants, top_blob);
+    if (packing == 1 && out_packing == 4)
+    {
+        VkMat dispatcher;
+        dispatcher.w = total;
+        dispatcher.h = 1;
+        dispatcher.c = 1;
+        cmd.record_pipeline(pipeline, bindings, constants, dispatcher);
+    }
+    else
+    {
+        cmd.record_pipeline(pipeline, bindings, constants, top_blob);
+    }
 
     return 0;
 }