Fix from review

Author: embhorn

src/tls.c

@@ -15260,13 +15260,18 @@ static int TLSX_Write(TLSX* list, byte* output, byte* semaphore,
         }
     }
 
-    if ((word32)*pOffset + (word32)offset > WOLFSSL_MAX_16BIT) {
-        WOLFSSL_MSG("TLSX_Write total extensions length exceeds word16");
-        return BUFFER_E;
+    /* Only validate and commit the aggregate offset when the loop
+     * completed without error; on the error path, leave *pOffset
+     * unchanged and return the original failure reason so callers
+     * see the real error instead of a masking BUFFER_E. */
+    if (ret == 0) {
+        if ((word32)*pOffset + (word32)offset > WOLFSSL_MAX_16BIT) {
+            WOLFSSL_MSG("TLSX_Write total extensions length exceeds word16");
+            return BUFFER_E;
+        }
+        *pOffset += offset;
     }
 
-    *pOffset += offset;
-
     return ret;
 }