Bug 1949969 - Fix the early return of `WSRunScanner::GetFirstVisibleP…

…oint` r=m_kato

It's obviously wrong, but I don't find how to make us hit here with the
traditional white-space normalizer, but this will cause new failure once
applying the patches for bug 1940377.  Therefore, this does not have a new
test, but it'll be tested by extant tests soon.

Differential Revision: https://phabricator.services.mozilla.com/D239270

editor/libeditor/WSRunScanner.cpp

@@ -356,7 +356,7 @@ EditorDOMPointType WSRunScanner::GetFirstVisiblePoint(
     const Element* aAncestorLimiter /* = nullptr */) {
   EditorDOMPoint atStartOfTextNode(&aTextNode, 0);
   if (!atStartOfTextNode.IsContainerEmpty() &&
-      atStartOfTextNode.IsCharCollapsibleASCIISpace()) {
+      !atStartOfTextNode.IsCharCollapsibleASCIISpace()) {
     return atStartOfTextNode.To<EditorDOMPointType>();
   }
   const TextFragmentData textFragmentData(