Fix that tabs where replaced with ? in search results

Looks like tabs are not "print", so make sure that whitespace is kept
unmodified.

Amends 1aa92b5dab

Fixes: QTCREATORBUG-26367
Change-Id: Ie9a89b36440c51ef2bbcf7a668f3c9b5f3c0f485
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: David Schulz <david.schulz@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/plugins/texteditor/basefilefind.cpp

@@ -236,7 +236,7 @@ static QString displayText(const QString &line)
     QString result = line;
     auto end = result.end();
     for (auto it = result.begin(); it != end; ++it) {
-        if (!it->isPrint())
+        if (!it->isSpace() && !it->isPrint())
             *it = QChar('?');
     }
     return result;