newly created field by set_field not visible to has_field test in same pipeline stage

newly created field by set_field not visible to has_field test in same pipeline stage

## Expected Behavior

newly create field by set_field should be immediately visible for has_field test in same stage

## Current Behavior

newly created field by set_field not visible to has_field test in same pipeline stage

## Steps to Reproduce (for bugs)

create the following pipeline, and input message will got field following_stage_visible and value being true, but no same_stage_visible field, which means the newly created new_field not visible to has_field test at same stage, only available to following stages.
```text
stage 0 match either
rule "always true";
rule "new_field visible to has_field at same stage";
stage 1 match all
rule "new_field visible to has_field at following stages";
end

rule "always true"
when
true
then
set_field("new_field","something");
end

rule "new_field visible to has_field at same stage"
when
has_field("new_field")
then
set_field("same_stage_visible", true);
end

rule "new_field visible to has_field at following stages"
when
has_field("new_field")
then
set_field("following_stage_visible", true);
end
```

## Your Environment

* Graylog Version: 2.4.3-1
* Elasticsearch Version: 5.6.8-1
* MongoDB Version: mongodb-enterprise-3.6.3-1
* Operating System: CentOS 7.4
* Browser version: firefox-52.7.2-1