fix header propagate bug

[azavadil]

In the typeSwitch function assignVal should be set to val for int16 case.
For the int64 case assignVal = "v" is correct because ParseInt returns an int64. Hence, no type cast is necessary. However for the int16 case a type cast is necessary.

Here is a concrete example of generated code without this change

if v, err := strconv.ParseInt(key, 10, 16); err == nil {
    val := int16(v)
    in.Request.CityId = &v
}

and the error

cannot use &v (type *int64) as type *int16 in assignment

[CLAassistant]

All committers have signed the CLA.

[coveralls]

Coverage remained the same at 67.62% when pulling f39ab07 on header-propogate-bug into 8eac3ef on master.