Fix comment count extraction due to 'K/M' postfixes

YouTube now displays 2K comments instead of 2359, for instance

youtube/__init__.py

@@ -54,7 +54,10 @@ def commatize(num):
     if num is None:
         return ''
     if isinstance(num, str):
-        num = int(num)
+        try:
+            num = int(num)
+        except ValueError:
+            return num
     return '{:,}'.format(num)