🩹 Compact fix for color generation in theme.json (#3222)

* Fix for incorrect theme.json generation of colours

* Fix for theme.json color generation

* Compact fix for colour theme.json generation

---------

Co-authored-by: Steve Jones <steve@codewithfeeling.com>

resources/js/build/wordpress.js

@@ -210,7 +210,8 @@ export function wordpressThemeJson({
         return;
       }
 
-      const rootContent = themeContent.slice(themeContent.indexOf('{') + 1, themeContent.lastIndexOf('}'))
+      const endIndex = themeContent.lastIndexOf('}');
+      const rootContent = themeContent.slice(themeContent.indexOf('{') + 1, endIndex === -1 ? undefined : endIndex);
       const colorVariables = {}
 
       const colorVarRegex = /--color-([^:]+):\s*([^;}]+)[;}]?/g