You missed 2,

Line +-683:
if (offset) {
cl = ngx_http_spdy_filter_get_shadow(stream, in->buf,
// offset, size);
(off_t) offset, (size_t) size);
if (cl == NULL) {
return NGX_CHAIN_ERROR;
}

and +-Line 760:
if (offset) {
// cl = ngx_http_spdy_filter_get_shadow(stream, in->buf, offset, size);
cl = ngx_http_spdy_filter_get_shadow(stream, in->buf, (off_t) offset, (size_t) size);
if (cl == NULL) {
return NGX_CHAIN_ERROR;
}


Additional warning +-line 684:
if (offset) {
cl = ngx_http_spdy_filter_get_shadow(stream, in->buf,
(off_t) offset, (size_t) size);
if (cl == NULL) {
return NGX_CHAIN_ERROR;
}

offset = 0;

src\http\ngx_http_spdy_filter_module.c(685): warning C4701: potentially uninitialized local variable 'cl' used

When I add +-line 629:
ngx_http_spdy_stream_t *stream;
ngx_http_spdy_loc_conf_t *slcf;
ngx_http_spdy_out_frame_t *frame;
+ cl = NULL;

The warning is gone.