Fix #1874 (calibre generated invalid epub)

src/calibre/ebooks/html.py

@@ -332,6 +332,8 @@ class PreProcessor(object):
                   (re.compile(r'&(\S+?);'), convert_entities),
                   # Remove the <![if/endif tags inserted by everybody's darling, MS Word
                   (re.compile(r'(?i)<{0,1}!\[(end){0,1}if[^>]*>'), lambda match: ''),
+                  # Replace ---> with --> since Adobe DE cries when it sees one
+                  (re.compile(r'-{3,}>'), lambda match : '-->'),
                   ]
                      
     # Fix pdftohtml markup