[libcalamares] Switch CStringPair key to QString

- the key is used in various places as a key for Qt data structures,
   so it's more convenient to have QString than a bare char*

src/libcalamares/locale/TimeZone.cpp

@@ -34,7 +34,7 @@ namespace Locale
 
 CStringPair::CStringPair( CStringPair&& t )
     : m_human( nullptr )
-    , m_key( nullptr )
+    , m_key()
 {
     // My pointers are initialized to nullptr
     std::swap( m_human, t.m_human );
@@ -43,7 +43,7 @@ CStringPair::CStringPair( CStringPair&& t )
 
 CStringPair::CStringPair( const CStringPair& t )
     : m_human( t.m_human ? strdup( t.m_human ) : nullptr )
-    , m_key( t.m_key ? strdup( t.m_key ) : nullptr )
+    , m_key( t.m_key )
 {
 }
 
@@ -76,7 +76,7 @@ munge( const char* s )
 
 CStringPair::CStringPair( const char* s1 )
     : m_human( s1 ? munge( s1 ) : nullptr )
-    , m_key( s1 ? strdup( s1 ) : nullptr )
+    , m_key( s1 ? QString( s1 ) : QString() )
 {
 }
 
@@ -84,7 +84,6 @@ CStringPair::CStringPair( const char* s1 )
 CStringPair::~CStringPair()
 {
     free( m_human );
-    free( m_key );
 }
 
 

src/libcalamares/locale/TimeZone.h

@@ -54,11 +54,11 @@ public:
     /// @brief Give the localized human-readable form
     virtual QString tr() const = 0;
 
-    const char* key() const { return m_key; }
+    QString key() const { return m_key; }
 
 protected:
     char* m_human = nullptr;
-    char* m_key = nullptr;
+    QString m_key;
 };
 
 /// @brief A pair of strings for timezone regions (e.g. "America")