Return generic helpURI if there are no CWEs

It can happen (by human error) that a rule may be missing CWEs in the warning text. So, to guard against that, if there are no CWEs, FlawFinder will generate and return a generic URI.

flawfinder.py

@@ -587,6 +587,8 @@ class Hit(object):
     # Help uri for each defined rule. e.g. "https://dwheeler.com/flawfinder#FF1002"
     # return first CWE link for now
     def helpuri(self):
+        if self.cwes() == '':
+            return 'https://dwheeler.com/flawfinder#{}'.format(self.ruleid)
         cwe = re.split(',|!', self.cwes())[0] + ")"
         return link_cwe_pattern.sub(
                 r'https://cwe.mitre.org/data/definitions/\2.html',