SC2016 gives false positive in parameter substitution

``` shell
#!/bin/sh
VAR=foo
echo "${VAR:+TEXT='$VAR'}"
```

it outputs here correctly: TEXT='foo'
(hitted it in a here-document, where we write out hmtl-code, e.g.

``` shell
#!/bin/sh
cat <<EOF
<body ${font_color:+ LINK='$font_color' VLINK='$font_color' ALINK='$font_color'}>
EOF
```
