generated sling configuration does not contain the variable

In some case the generated sling configuration files is wrong.

To reproduce the bug:

1. prepare a handelbar template

   com.example.ServiceConfiguration {{#if bar}} bar="{{bar}}"{{/if}} {{#if foo}} foo="{{foo}}"{{/if}}

2. define only the configuration "foo" in the environment and "bar" not.

   config: foo: "foo"

Expectation: a sling configuration file is generated:

com.example.ServiceConfiguration.config

Actual: 2 configuration files are generated.

• com.example.ServiceConfiguration.config (the file is empty)

• foo="foo".config (the file is empty)