[LyX/master] Revert "Remove workaround that is not needed anymore with Qt 5.12"

[Jean-Marc Lasgouttes]

commit e30758166e8fccbc9546e4782caf4c5fa4d1a7d4
Author: Jean-Marc Lasgouttes <lasgouttes at lyx.org>
Date:   Wed Oct 30 19:31:59 2024 +0100

    Revert "Remove workaround that is not needed anymore with Qt 5.12"
    
    We want to support Qt 5.9 for now.
    
    This reverts commit 8837f8ca8ca5e1d87a846871aa0860af0dbf6ae5.
---
 src/frontends/qt/GuiLyXFiles.cpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/frontends/qt/GuiLyXFiles.cpp b/src/frontends/qt/GuiLyXFiles.cpp
index ab30295eea..a93000c3c6 100644
--- a/src/frontends/qt/GuiLyXFiles.cpp
+++ b/src/frontends/qt/GuiLyXFiles.cpp
@@ -613,7 +613,12 @@ void GuiLyXFiles::passParams(string const & data)
 
 void GuiLyXFiles::selectItem(QString const & item)
 {
-	QList<QTreeWidgetItem *> twi = filesLW->findItems(item, Qt::MatchExactly | Qt::MatchRecursive);
+	/* Using an intermediary variable flags is needed up to at least
+	 * Qt 5.5 because of a subtle namespace issue. See:
+	 *   https://stackoverflow.com/questions/10755058/qflags-enum-type-conversion-fails-all-of-a-sudden
+	 * for details.*/
+	Qt::MatchFlags const flags(Qt::MatchExactly|Qt::MatchRecursive);
+	QList<QTreeWidgetItem *> twi = filesLW->findItems(item, flags);
 	if (!twi.isEmpty())
 		twi.first()->setSelected(true);
 }