fix SetQuery panic (caused by uninitialized map)

`api.Res("someresource").SetQuery(query)` will panics. Caused by lost `UrlValues` map in call chain.

```
panic: runtime error: assignment to entry in nil map

goroutine 16 [running]:
runtime.panic(0x72f0c0, 0x93f753)
	/usr/lib/go/src/pkg/runtime/panic.c:279 +0xf5
github.com/bndr/gopencils.(*Resource).SetQuery(0xc208004660, 0xc20807bc20, 0x2)
	/home/s.seletskiy/.go/src/github.com/bndr/gopencils/resource.go:87 +0x176
```