Fix %d and empty default in outtmpl

Closes #388

yt_dlp/YoutubeDL.py

@@ -936,7 +936,8 @@ class YoutubeDL(object):
                     # If value is an object, sanitize might convert it to a string
                     # So we convert it to repr first
                     value, fmt = repr(value), '%ss' % fmt[:-1]
-                value = sanitize(key, value)
+                if fmt[-1] in 'csr':
+                    value = sanitize(key, value)
             tmpl_dict[key] = value
             return '%({key}){fmt}'.format(key=key, fmt=fmt)
 

yt_dlp/utils.py

@@ -2107,6 +2107,8 @@ def sanitize_filename(s, restricted=False, is_id=False):
             return '_'
         return char
 
+    if s == '':
+        return ''
     # Handle timestamps
     s = re.sub(r'[0-9]+(?::[0-9]+)+', lambda m: m.group(0).replace(':', '_'), s)
     result = ''.join(map(replace_insane, s))