Do not stop on malformed xml

[tigre-bleu]

nMap_Merger quits with the following exception when an xml file is malformed:

Traceback (most recent call last):
  File "/usr/local/bin/nmap-merger", line 157, in <module>
    main_nMapMerger(s)
  File "/usr/local/bin/nmap-merger", line 103, in main_nMapMerger
    H = merge_nMap(xml,mergeFile)
  File "/usr/local/bin/nmap-merger", line 31, in merge_nMap
    nMapXML = ET.parse(f)
  File "/usr/lib/python3.9/xml/etree/ElementTree.py", line 1229, in parse
    tree.parse(source, parser)
  File "/usr/lib/python3.9/xml/etree/ElementTree.py", line 580, in parse
    self._root = parser._parse_whole(source)
xml.etree.ElementTree.ParseError: no element found: line 69, column 0

It should be better to handle gracefully by printing a warning and continuing with other files.