Fixed off-by-one in xslt parameter parsing.

The problem was introduced in 0.7.44 (r2589) during conversion to complex
values.  Previously string.len included space for terminating NUL, but
with complex values it doesn't.

src/http/modules/ngx_http_xslt_filter_module.c

@@ -585,7 +585,7 @@ ngx_http_xslt_params(ngx_http_request_t *r, ngx_http_xslt_filter_ctx_t *ctx,
                        "xslt filter param: \"%s\"", string.data);
 
         p = string.data;
-        last = string.data + string.len - 1;
+        last = string.data + string.len;
 
         while (p && *p) {