PDF Metadata: When choosing between reading metadata from the Info dict

and the XMP block, consider both the MetadataData and the ModifyDate in
the XMP block, since there exist PDF metadata writing tools that update
one and not the other. See #1440304 ([Enhancement] configure metadata import when importing pdf file in calibre)

src/calibre/ebooks/metadata/xmp.py

@@ -199,6 +199,23 @@ def read_xmp_identifers(parent):
         else:
             yield scheme[0].text or '', value
 
+def safe_parse_date(raw):
+    if raw:
+        try:
+            return parse_date(raw)
+        except Exception:
+            pass
+
+def more_recent(one, two):
+    if one is None:
+        return two
+    if two is None:
+        return one
+    try:
+        return max(one, two)
+    except Exception:
+        return one
+
 def metadata_from_xmp_packet(raw_bytes):
     root = parse_xmp_packet(raw_bytes)
     mi = Metadata(_('Unknown'))
@@ -226,12 +243,11 @@ def metadata_from_xmp_packet(raw_bytes):
     bkp = first_simple('//xmp:CreatorTool', root)
     if bkp:
         mi.book_producer = bkp
-    md = first_simple('//xmp:MetadataDate', root)
+    md = safe_parse_date(first_simple('//xmp:MetadataDate', root))
-    if md:
+    mod = safe_parse_date(first_simple('//xmp:ModifyDate', root))
-        try:
+    fd = more_recent(md, mod)
-            mi.metadata_date = parse_date(md)
+    if fd is not None:
-        except:
+        mi.metadata_date = fd
-            pass
     rating = first_simple('//calibre:rating', root)
     if rating is not None:
         try:
@@ -311,7 +327,7 @@ def consolidate_metadata(info_mi, info):
     if 'ModDate' in info and hasattr(xmp_mi, 'metadata_date'):
         try:
             info_date = parse_date(info['ModDate'])
-        except:
+        except Exception:
             pass
         else:
             prefer_info = info_date > xmp_mi.metadata_date