change: use nil instead of false when lpush&rpush overflow.

Co-authered-by: lijunlong<lijunlong@openresty.com>

Author: hy05190134

src/ngx_http_lua_shdict.c

@@ -943,7 +943,7 @@ ngx_http_lua_shdict_push_helper(lua_State *L, int flags)
 
         ngx_shmtx_unlock(&ctx->shpool->mutex);
 
-        lua_pushboolean(L, 0);
+        lua_pushnil(L);
         lua_pushliteral(L, "no memory");
         return 2;
     }

t/145-shdict-list.t

@@ -827,3 +827,27 @@ GET /test
 aa list value: nil
 --- no_error_log
 [error]
+
+
+
+=== TEST 22: lpush return nil
+--- http_config
+    lua_shared_dict dogs 100k;
+--- config
+    location = /test {
+        content_by_lua_block {
+            local dogs = ngx.shared.dogs
+            for i = 1, 2920
+            do
+                local len, err = dogs:lpush("foo", "bar")
+            end
+            local len, err = dogs:lpush("foo", "bar")
+            ngx.say(len)
+        }
+    }
+--- request
+GET /test
+--- response_body
+nil
+--- no_error_log
+[error]