Try to fix compil issue on OSX (commit 8757fcf6 breaks the import gfx dialog)

pcbnew/import_gfx/dxf_import_plugin.h

@@ -145,8 +145,9 @@ public:
 
     const wxArrayString GetFileExtensions() const override
     {
-        // N.B. The extra "" hints for some compilers that the array should not be optimized out
-        return wxArrayString( 1, { "dxf", "" } );
+        wxArrayString list;
+        list.Add( "dxf" );
+        return list;
     }
 
     bool Load( const wxString& aFileName ) override;

pcbnew/import_gfx/svg_import_plugin.h

@@ -44,8 +44,9 @@ public:
 
     const wxArrayString GetFileExtensions() const override
     {
-        // N.B. The extra "" hints for some compilers that the array should not be optimized out
-        return wxArrayString( 1, { "svg", "" } );
+        wxArrayString list;
+        list.Add( "svg" );
+        return list;
     }
 
     /**