Rename wxLocaleIdent::IsDefault() to IsEmpty()

We don't use empty wxLocaleIdent as default user locale and it doesn't
make much sense to do it, as the default locale is already accessible
via wxUILocale::GetDefault().

include/wx/uilocale.h

@@ -33,7 +33,7 @@ enum
 class WXDLLIMPEXP_BASE wxLocaleIdent
 {
 public:
-    // Leave language empty
+    // Default ctor creates an empty, invalid identifier.
     wxLocaleIdent() { }
 
     // Construct from language, i.e. a two-letter ISO 639-1 code (or a
@@ -69,8 +69,8 @@ public:
     // Construct platform dependent name
     wxString GetName() const;
 
-    // Empty language represents user's default language
-    bool IsDefault() const
+    // Empty locale identifier is invalid. at least Language() must be called.
+    bool IsEmpty() const
     {
         return m_language.empty();
     }

interface/wx/uilocale.h

@@ -214,7 +214,9 @@ class wxLocaleIdent
 {
 public:
     /**
-        This is the default constructor and it leaves language empty.
+        Default constructor creates an empty and invalid locale identifier.
+
+        At least Language() must be called to make the identifier valid.
     */
     wxLocaleIdent();
 
@@ -318,9 +320,9 @@ public:
     wxString GetName() const;
 
     /**
-        Empty language represents user's default language.
+        Check if the locale is empty.
 
-        @return @true if language is empty, @false otherwise.
+        @return @true if this is an empty, invalid object.
     */
-    bool IsDefault() const;
+    bool IsEmpty() const;
 };

src/unix/uilocale.cpp

@@ -261,7 +261,7 @@ wxUILocaleImplUnix::~wxUILocaleImplUnix()
 void
 wxUILocaleImplUnix::Use()
 {
-    if ( m_locId.IsDefault() )
+    if ( m_locId.IsEmpty() )
     {
         // This is the default locale, it is already in use.
         return;