From 30f65e0ebac0afb344e96a1f15757f65287f1c98 Mon Sep 17 00:00:00 2001
From: John Schember <john@nachtimwald.com>
Date: Fri, 21 Jan 2011 08:51:48 -0500
Subject: [PATCH] GUI: Regex Test, clear matched items when no regex is
 present. Speed up clearing by not running regex matching on empty patterns.

---
 src/calibre/gui2/convert/regex_builder.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/calibre/gui2/convert/regex_builder.py b/src/calibre/gui2/convert/regex_builder.py
index c5c8d84a88..ca6e429176 100644
--- a/src/calibre/gui2/convert/regex_builder.py
+++ b/src/calibre/gui2/convert/regex_builder.py
@@ -47,6 +47,8 @@ class RegexBuilder(QDialog, Ui_RegexBuilder):
                 return False
         else:
             self.regex.setStyleSheet('QLineEdit { color: black; background-color: white; }')
+            self.preview.setExtraSelections([])
+            return False
         return True
 
     def do_test(self):