issue: #29419
* If a sparse vector with 0 non-zero value is inserted, no ANN search on
this sparse vector field will return it as a result. User may retrieve
this row via scalar query or ANN search on another vector field though.
* If the user uses an empty sparse vector as the query vector for a ANN
search, no neighbor will be returned.
Signed-off-by: Buqian Zheng <zhengbuqian@gmail.com>