Decoding text: catch exception

Wrapped the decode instruction derived from
change Ia2051a2a80851b15b1a04a135763291bd633d4e3
in a "try: except:" block, as suggested in comment 9 of bug 67410

Also: added a comma in "self.CHARSET" regex in case of
"contentType" contains a list of value from HTML-meta

Change-Id: I3af86d3386ea919001287fe1c057932c16537eb4