[brightcove] Fix extraction of embedded videos

There was a leading ‘:’ in the regex.
The ‘flashvars’ parameter is not always available.

youtube_dl/extractor/brightcove.py

@@ -90,9 +90,12 @@ class BrightcoveIE(InfoExtractor):
         object_doc = xml.etree.ElementTree.fromstring(object_str)
 
         fv_el = find_xpath_attr(object_doc, './param', 'name', 'flashVars')
+        if fv_el is not None:
             flashvars = dict(
                 (k, v[0])
                 for k, v in compat_parse_qs(fv_el.attrib['value']).items())
+        else:
+            flashvars = {}
 
         def find_param(name):
             if name in flashvars:
@@ -131,7 +134,7 @@ class BrightcoveIE(InfoExtractor):
         m_brightcove = re.search(
             r'''(?sx)<object
             (?:
-                :[^>]+?class=([\'"])[^>]*?BrightcoveExperience.*?\1 |
+                [^>]+?class=([\'"])[^>]*?BrightcoveExperience.*?\1 |
                 [^>]*?>\s*<param\s+name="movie"\s+value="https?://[^/]*brightcove\.com/
             ).+?</object>''',
             webpage)