Fix --runemptysuite not working for dynamic empty suite

[jnhyperion]

• ws/empty1.robot

*** Settings ***
Library         DataDriver    file=ws/foo.json    delimiter=comma

*** Test Cases ***
example
    [Template]    My Kw
*** Keywords ***
my kw
     No Operation

• ws/empty2.robot

*** Settings ***
Library         DataDriver    file=ws/foo.json    delimiter=comma

*** Test Cases ***
example
    [Template]    My Kw
*** Keywords ***
my kw
     No Operation

• ws/empty3.robot

*** Settings ***
Library         DataDriver    file=ws/foo.json    delimiter=comma

*** Test Cases ***
example
    [Template]    My Kw
*** Keywords ***
my kw
     No Operation

• data.json

[]

• run pabot --processes 8 --runemptysuite ws

before fix:
Output: /Users/jnhuang/github/pabot/output.xml
[ ERROR ] Suite 'Ws' contains no tests after model modifiers.

Try --help for usage information. ...

after fix:
no errors raised, generated empty report