[util] generalize 'build_duration_func'

gallery_dl/text.py

@@ -209,11 +209,12 @@ def _hex_to_char(match):
 
 def parse_bytes(value, default=0, suffixes="bkmgtp"):
     """Convert a bytes-amount ("500k", "2.5M", ...) to int"""
-    try:
-        last = value[-1].lower()
-    except Exception:
+    if not value:
         return default
 
+    value = str(value).strip()
+    last = value[-1].lower()
+
     if last in suffixes:
         mul = 1024 ** suffixes.index(last)
         value = value[:-1]