error if '()' is used as regexp search pattern in 'Search in project' dialog

[Andrey Skvortsov]

Steps to reproduce:

1. Open any project
2. Go to Edit->Search in project dialog
3. Enable search for regular expression
4. Enter following pattern '()' (without quotes)
5. Click 'Find'

Following traceback happens:

Traceback (most recent call last):
File "/home/developer/WorkData/PLC/beremiz/beremiz/IDEFrame.py", line 1291, in OnSearchInProjectMenu
self.SearchResultPanel.SetSearchResults(criteria, result)
File "/home/developer/WorkData/PLC/beremiz/beremiz/controls/SearchResultPanel.py", line 158, in SetSearchResults
self.RefreshView()
File "/home/developer/WorkData/PLC/beremiz/beremiz/controls/SearchResultPanel.py", line 250, in RefreshView
self.GenerateSearchResultsTreeBranch(root, search_results_tree_infos)
File "/home/developer/WorkData/PLC/beremiz/beremiz/controls/SearchResultPanel.py", line 318, in GenerateSearchResultsTreeBranch
self.GenerateSearchResultsTreeBranch(item, child)
File "/home/developer/WorkData/PLC/beremiz/beremiz/controls/SearchResultPanel.py", line 318, in GenerateSearchResultsTreeBranch
self.GenerateSearchResultsTreeBranch(item, child)
File "/home/developer/WorkData/PLC/beremiz/beremiz/controls/SearchResultPanel.py", line 307, in GenerateSearchResultsTreeBranch
text_ctrl.SetStyle(start_idx, end_idx, style)
File "/usr/lib/python2.7/dist-packages/wx-3.0-gtk2/wx/_core.py", line 13414, in SetStyle
return core.TextAreaBase_SetStyle(*args, **kwargs)
PyAssertionError: C++ assertion "start >= 0 && end <= l" failed at ../src/gtk/textctrl.cpp(1743) in SetStyle(): invalid range in wxTextCtrl::SetStyle