Fix null column on scripted values

[klahnakoski]

The following query shows a count > 0 in the null row when it should not. The cause appears to be in the missing ES filter; which is not inverting scripted values properly.

Please

1. Make a test
2. Check if the problem still exists on the new cluster
3. Fix it

{
	"from":"coverage",
	"where":{"and":[
		{"prefix":{"source.file.name":"mfbt/"}},
		{"eq":{"repo.changeset.id12":"752465b44c79"}}
	]},
	"groupby":[{
		"name":"subdir",
		"value":{
			"then":{"between":{"source.file.name":["mfbt/","/"]}},
			"when":{"start":5,"find":{"source.file.name":"/"}},
			"else":{"not_left":{"source.file.name":5}}
		}
	}],
	"select":[
		{"aggregate":"count"},
	],
	"limit":10000
}

[klahnakoski]

fixed with #92