[locale] Fix interpretation of configured selector

- In GeoIP handler constructors that take a string (to configure the
   selector to use), interpret the empty string (which generally isn't
   a meaningful selector) as meaning "use the default".
 - Drop the no-argument constructors in favor of a default-argument
   which is empty.

src/modules/locale/GeoIPJSON.cpp

@@ -27,16 +27,10 @@
 #include <yaml-cpp/yaml.h>
 
 GeoIPJSON::GeoIPJSON(const QString& attribute)
-    : GeoIP( attribute )
+    : GeoIP( attribute.isEmpty() ? QLatin1String( "time_zone" ) : attribute )
 {
 }
 
-GeoIPJSON::GeoIPJSON()
-    : GeoIPJSON( QLatin1Literal( "time_zone" ) )
-{
-}
-
-
 GeoIP::RegionZonePair
 GeoIPJSON::processReply( const QByteArray& data )
 {

src/modules/locale/GeoIPJSON.h

@@ -31,8 +31,12 @@
 class GeoIPJSON : public GeoIP
 {
 public:
-    explicit GeoIPJSON( const QString& attribute );
-    explicit GeoIPJSON();
+    /** @brief Configure the attribute name which is selected.
+     *
+     * If an empty string is passed in (not a valid attribute name),
+     * then "time_zone" is used.
+     */
+    explicit GeoIPJSON( const QString& attribute = QString() );
 
     virtual RegionZonePair processReply( const QByteArray& );
 } ;

src/modules/locale/GeoIPXML.cpp

@@ -24,16 +24,10 @@
 #include <QtXml/QDomDocument>
 
 GeoIPXML::GeoIPXML( const QString& element )
-    : GeoIP( element )
+    : GeoIP( element.isEmpty() ? QLatin1String( "TimeZone" ) : element )
 {
 }
 
-GeoIPXML::GeoIPXML()
-    : GeoIPXML( QLatin1Literal( "TimeZone" ) )
-{
-}
-
-
 GeoIP::RegionZonePair
 GeoIPXML::processReply( const QByteArray& data )
 {

src/modules/locale/GeoIPXML.h

@@ -31,10 +31,12 @@
 class GeoIPXML : public GeoIP
 {
 public:
-    /** @brief Configure the element name which is selected. */
-    explicit GeoIPXML( const QString& element );
-    /** @brief Use default TimeZone element. */
-    explicit GeoIPXML();
+    /** @brief Configure the element tag which is selected.
+     *
+     * If an empty string is passed in (not a valid element tag),
+     * then "TimeZone" is used.
+     */
+    explicit GeoIPXML( const QString& element = QString() );
 
     virtual RegionZonePair processReply( const QByteArray& );
 } ;