Slice struct with all "omitempty" fields set to zero value ​​will generate wrong data

[ljfuyuan]

look at this sample below:

type Sample struct {
    K        uint32 `msg:"k,omitempty"`
        V        uint32 `msg:"v,omitempty"`
}

type Samples []Sample

and now we construct a set of test cases:

s := Samples{
        {1, 1},
        {0, 0},
        {3, 3},
    }

and the generated code is:

    for za0001 := range z {
        // check for omitted fields
        zb0001Len := uint32(2)
        var zb0001Mask uint8 /* 2 bits */
        _ = zb0001Mask
        if z[za0001].K == 0 {
            zb0001Len--
            zb0001Mask |= 0x1
        }
        if z[za0001].V == 0 {
            zb0001Len--
            zb0001Mask |= 0x2
        }
        // variable map header, size zb0001Len
        o = append(o, 0x80|uint8(zb0001Len))
        if zb0001Len == 0 {
            return     //  <---- !!! When looping to the second element, wrong data will be generated due to return. Continue may be used here. 

        }
...... ignore

[klauspost]

Please try #377