fix: handle undefined language properties in findLanguageCodesForDuplicateLabels

Fixes FORMBRICKS-E5

- Add safe null/undefined checks before calling .trim() on i18n string values
- Use type guard to filter out undefined or empty string values
- Prevents TypeError when language property doesn't exist in TI18nString object
- Aligns with the safer implementation already present in elements-validation.ts

packages/types/surveys/validation.ts

@@ -224,7 +224,10 @@ export const findLanguageCodesForDuplicateLabels = (
   const duplicateLabels = new Set<string>();
 
   for (const language of languagesToCheck) {
-    const labelTexts = labels.map((label) => label[language].trim()).filter(Boolean);
+    const labelTexts = labels
+      .map((label) => label[language])
+      .filter((text): text is string => typeof text === "string" && text.trim().length > 0)
+      .map((text) => text.trim());
     const uniqueLabels = new Set(labelTexts);
 
     if (uniqueLabels.size !== labelTexts.length) {