fix(frontend): out of credits when credits null (#2804)

# Description

Please include a summary of the changes and the related issue. Please
also include relevant motivation and context.

## Checklist before requesting a review

Please delete options that are not relevant.

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented hard-to-understand areas
- [ ] I have ideally added tests that prove my fix is effective or that
my feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged

## Screenshots (if appropriate):

frontend/lib/components/CurrentBrain/CurrentBrain.tsx

@@ -18,7 +18,7 @@ export const CurrentBrain = ({
     setCurrentBrainId(null);
   };
 
-  if (!remainingCredits) {
+  if (remainingCredits === 0) {
     return (
       <div className={styles.no_credits_left}>
         <span>