Help/litehtml: Fix resolution of font name

- check case-insensitively
- need to break after the first font was found in database

Change-Id: Iddd58ec88d61b2506965a618441205e8176e383f
Reviewed-by: hjk <hjk@qt.io>

src/plugins/help/qlitehtml/container_qpainter.cpp

@@ -40,6 +40,7 @@
 #include <QUrl>
 
 #include <algorithm>
+#include <set>
 
 const int kDragDistance = 5;
 
@@ -453,11 +454,24 @@ litehtml::uint_ptr DocumentContainer::create_font(const litehtml::tchar_t *faceN
 #if (QT_VERSION >= QT_VERSION_CHECK(5, 13, 0))
     font->setFamilies(familyNames);
 #else
-    static const auto knownFamilies = QFontDatabase().families().toSet();
+    struct CompareCaseinsensitive
+    {
+        bool operator()(const QString &a, const QString &b) const
+        {
+            return a.compare(b, Qt::CaseInsensitive) < 0;
+        }
+    };
+    static const QStringList known = QFontDatabase().families();
+    static const std::set<QString, CompareCaseinsensitive> knownFamilies(known.cbegin(),
+                                                                         known.cend());
     font->setFamily(familyNames.last());
-    for (const QString &name : qAsConst(familyNames))
+    for (const QString &name : qAsConst(familyNames)) {
-        if (knownFamilies.contains(name))
+        const auto found = knownFamilies.find(name);
-            font->setFamily(name);
+        if (found != knownFamilies.end()) {
+            font->setFamily(*found);
+            break;
+        }
+    }
 #endif
     font->setPixelSize(size);
     font->setWeight(cssWeightToQtWeight(weight));