handle the empty URL case in file picker

Some extensions in the wild, for example Impress Photo Album Creator,
manage to call the file picker dialog with an empty URL. The resulting
error message is not very helpful: "Operation not supported" dialog.
Therefore we assign a default URL when empty URL is passed.

Change-Id: Icf71142411a79e1fe2d1d5918d2a400b174acc00
Reviewed-on: https://gerrit.libreoffice.org/2390Reviewed-by: Andras Timar <atimar@suse.com>
Tested-by: Andras Timar <atimar@suse.com>

vcl/unx/gtk/fpicker/SalGtkFolderPicker.cxx

@@ -78,6 +78,9 @@ void SAL_CALL SalGtkFolderPicker::setDisplayDirectory( const rtl::OUString& aDir
     OSL_ASSERT( m_pDialog != NULL );
 
     OString aTxt = unicodetouri( aDirectory );
+    if( aTxt.isEmpty() ){
+      aTxt = unicodetouri(OUString("file:///."));
+    }
 
     if( !aTxt.isEmpty() && aTxt.lastIndexOf('/') == aTxt.getLength() - 1 )
         aTxt = aTxt.copy( 0, aTxt.getLength() - 1 );

vcl/unx/gtk/fpicker/SalGtkPicker.cxx

@@ -217,6 +217,9 @@ void SAL_CALL SalGtkPicker::implsetDisplayDirectory( const rtl::OUString& aDirec
     OSL_ASSERT( m_pDialog != NULL );
 
     OString aTxt = unicodetouri(aDirectory);
+    if( aTxt.isEmpty() ){
+      aTxt = unicodetouri(OUString("file:///."));
+    }
 
     if( aTxt.lastIndexOf('/') == aTxt.getLength() - 1 )
         aTxt = aTxt.copy( 0, aTxt.getLength() - 1 );