fix(caret): getting last letter top in long multiline words (@NadAlaba)…

… (#5856)

* fix(caret): getting last letter top in long multiline words (@NadAlaba)

* no need to check for invisible extra letters

This check was needed when `letterPosTop` was
`currentLetter?.offsetTop ?? previousLetter?.offsetTop ??
lastWordLetter?.offsetTop` where `previousLetter?.offsetTop` was defined
but 0 in extra letters in blind mode, so we got the value of zero
although in some fonts the real value (`lastWordLetter` value) is not 0.

However, now we don't use `previousLetter`, and `currentLetter` is
undefined in extra letters (blind mode or not), so we'll get the value
we want (`lastWordLetter` value) in extra letters.

* update comment

frontend/src/ts/test/caret.ts

@@ -159,14 +159,15 @@ export async function updatePosition(noAnim = false): Promise<void> {
   const isLanguageRightToLeft = currentLanguage.rightToLeft;
 
   // in blind mode, and hide extra letters, extra letters have zero offsets
-  // offsetTop and offsetHeight is the same for all visible letters
+  // offsetHeight is the same for all visible letters
+  // so is offsetTop (for same line letters)
   const letterHeight =
     currentLetter?.offsetHeight ||
     lastWordLetter?.offsetHeight ||
     Config.fontSize * Numbers.convertRemToPixels(1);
 
   const letterPosTop =
-    currentLetter?.offsetTop || lastWordLetter?.offsetTop || 0;
+    currentLetter?.offsetTop ?? lastWordLetter?.offsetTop ?? 0;
   const diff = letterHeight - caret.offsetHeight;
   let newTop = activeWordEl.offsetTop + letterPosTop + diff / 2;
   if (Config.caretStyle === "underline") {