Fix GUI dialog errors preventing them from returning properly.

src/calibre/gui2/convert/heuristics.py

@@ -34,8 +34,11 @@ def __init__(self, parent, get_option, get_help, db=None, book_id=None):
     def break_cycles(self):
         Widget.break_cycles(self)
         
-        self.opt_enable_heuristics.stateChanged.disconnect()
-        self.opt_unwrap_lines.stateChanged.disconnect()
+        try:
+            self.opt_enable_heuristics.stateChanged.disconnect()
+            self.opt_unwrap_lines.stateChanged.disconnect()
+        except:
+            pass
         
     def set_value_handler(self, g, val):
         if val is None and g is self.opt_html_unwrap_factor:

src/calibre/gui2/convert/search_and_replace.py

@@ -45,5 +45,4 @@ def pre_commit_check(self):
                 error_dialog(self, _('Invalid regular expression'),
                              _('Invalid regular expression: %s')%err).exec_()
                 return False
-            
-
+        return True