Jester Crashes when locks module imported after jester module
``` nim
when hostOs == "linux":
    {.passL: "-pthread".}

import asyncdispatch
import jester
import locks

routes:
    get "/":

        let st = newStringTable()
        try:
            let x = st["x"]
        except:
            echo "NOt FOUND x"
            let mytab = newStringTable({"key1": "val1", "key2": "val2"},
                                       modeCaseInsensitive)
            echo "MYTAB: ", mytab

        try:
            let x = st["x"]
        except:
            echo "NOt FOUND x"
            let mytab = newStringTable({"key1": "val1", "key2": "val2"},
                                       modeCaseInsensitive)
            echo "MYTAB: ", mytab


        resp Http200, """{"result": -1}"""

    settings.port = Port(4000)

runForever()
```

Steps to reproduce:
  1) Run the example in order to reproduce the bug: `nim c -r main.nim`
  2) Enter localhost:4000/ in browser.
