Prevent artefacts of imported transactions from showing

When you start the import process, possible imported transactions are
displayed in the source open register and if you deselect any and press
the OK button you are left with blank lines in the register for those
deselected so move the gnc_gen_trans_list_delete to before the gui
refresh call.

gnucash/import-export/import-main-matcher.c

@@ -214,10 +214,11 @@ on_matcher_ok_clicked (GtkButton *button, GNCImportMainMatcher *info)
     }
     while (gtk_tree_model_iter_next (model, &iter));
 
+    gnc_gen_trans_list_delete (info);
+
     /* Allow GUI refresh again. */
     gnc_resume_gui_refresh();
 
-    gnc_gen_trans_list_delete (info);
     /* DEBUG ("End") */
 }