wxGUI/datacatalog: fix incorrect entry invalid (broken) regular expression

[tmszi]

To Reproduce:

Steps to reproduce the behavior:

1. Launch wxGUI
2. On the Data page (tab) write e.g. asterisk symbol in the search widget
3. See error message

Traceback (most recent call last):
  File
"/usr/lib64/grass79/gui/wxpython/datacatalog/toolbars.py",
line 68, in <lambda>

self.filter.GetValue(), self.filter_element))
  File
"/usr/lib64/grass79/gui/wxpython/datacatalog/catalog.py",
line 142, in Filter

self.tree.Filter(text=text, element=element)
  File
"/usr/lib64/grass79/gui/wxpython/datacatalog/tree.py", line
1663, in Filter

self._model = self._orig_model.Filtered(method='filtering',
name=re.compile(name))
  File "/usr/lib64/python3.6/re.py", line 233, in compile

return _compile(pattern, flags)
  File "/usr/lib64/python3.6/re.py", line 301, in _compile

p = sre_compile.compile(pattern, flags)
  File "/usr/lib64/python3.6/sre_compile.py", line 562, in
compile

p = sre_parse.parse(p, flags)
  File "/usr/lib64/python3.6/sre_parse.py", line 855, in
parse

p = _parse_sub(source, pattern, flags & SRE_FLAG_VERBOSE, 0)
  File "/usr/lib64/python3.6/sre_parse.py", line 416, in
_parse_sub

not nested and not items))
  File "/usr/lib64/python3.6/sre_parse.py", line 616, in
_parse

source.tell() - here + len(this))
sre_constants
.
error
:
nothing to repeat at position 0

[petrasovaa]

Thanks for catching this!