Check for selectorText undefined, pull out inline regex

Guarding against undefined selectorText and pulling out an inline regex in the deckgrid style check loop.

scss/sass generates CSS rule(s) without selectorText a la: 
```
CSSMediaRule {
  cssRules: CSSRuleList, 
  media: MediaList, 
  parentRule: CSSMediaRule, 
  parentStyleSheet: CSSStyleSheet, 
  cssText: "@media -sass-debug-info {
    filename { font-famil…/_reset.scss'; }
    line { font-family: '213'; }
  }"
…}
```