[libcalamares] CStringList::find() convenience function

- search for a key and return a type-cast pointer to the result
 - while here, simplify some other code
 - the find() function could be done with std::find_if but doesn't
   get any shorter or more elegant

src/libcalamares/locale/TimeZone.h

@@ -66,7 +66,22 @@ protected:
     QString m_key;
 };
 
-using CStringPairList = QList< CStringPair* >;
+class CStringPairList : public QList< CStringPair* >
+{
+public:
+    template < typename T >
+    T* find( const QString& key ) const
+    {
+        for ( auto* p : *this )
+        {
+            if ( p->key() == key )
+            {
+                return dynamic_cast< T* >( p );
+            }
+        }
+        return nullptr;
+    }
+};
 
 /// @brief A pair of strings for timezone regions (e.g. "America")
 class TZRegion : public CStringPair
@@ -90,6 +105,8 @@ public:
     /// @brief Calls fromFile with the standard zone.tab name
     static CStringPairList fromZoneTab();
 
+    const CStringPairList& zones() const { return m_zones; }
+
 private:
     CStringPairList m_zones;
 };

src/modules/locale/LocalePage.cpp

@@ -147,10 +147,13 @@ containsLocation( const QList< LocaleGlobal::Location >& locations, const QStrin
 void
 LocalePage::init( const QString& initialRegion, const QString& initialZone, const QString& localeGenPath )
 {
-    m_regionList = CalamaresUtils::Locale::TZRegion::fromZoneTab();
-    m_regionModel = std::make_unique< CalamaresUtils::Locale::CStringListModel >( m_regionList );
+    using namespace CalamaresUtils::Locale;
+
+    m_regionList = TZRegion::fromZoneTab();
+    m_regionModel = std::make_unique< CStringListModel >( m_regionList );
     m_regionCombo->setModel( m_regionModel.get() );
 
+
     // Setup locations
     QHash< QString, QList< LocaleGlobal::Location > > regions = LocaleGlobal::getLocations();
 
@@ -159,7 +162,8 @@ LocalePage::init( const QString& initialRegion, const QString& initialZone, cons
 
     m_regionCombo->currentIndexChanged( m_regionCombo->currentIndex() );
 
-    if ( keys.contains( initialRegion ) && containsLocation( regions.value( initialRegion ), initialZone ) )
+    auto* region = m_regionList.find< TZRegion >( initialRegion );
+    if ( region && region->zones().find< TZZone >( initialZone ) )
     {
         m_tzWidget->setCurrentLocation( initialRegion, initialZone );
     }