Don't try to get a translated empty string

Hashing an empty string can be crashy.  And empty strings are reserved
in gettext, so we shouldn't try.

Fixes https://gitlab.com/kicad/code/kicad/-/issues/15354

common/tool/tool_action.cpp

@@ -123,6 +123,9 @@ TOOL_EVENT TOOL_ACTION::MakeEvent() const
 
 wxString TOOL_ACTION::GetLabel() const
 {
+    if( m_label.empty() )
+        return wxEmptyString;
+
     return wxGetTranslation( m_label );
 }
 

include/tool/tool_action.h

@@ -299,6 +299,9 @@ public:
      */
     TOOL_EVENT MakeEvent() const;
 
+    /**
+     * Return the translated label for the action.
+    */
     wxString GetLabel() const;
     wxString GetMenuItem() const;
     wxString GetTooltip( bool aIncludeHotkey = true ) const;