Resolve SOURCE_DATE_EPOCH=0 bug.

Not clear to me if...

* There may also be a timezone issue here leading to the negative value.

And furthermore...

* Non-integer values will still raise an exception here.

But this does at least resolve the immediate issue.

Author: lovelydinosaur

mkdocs/utils/__init__.py

@@ -56,7 +56,7 @@ def get_build_timestamp(*, pages: Collection[Page] | None = None) -> int:
         dt = datetime.fromisoformat(date_string)
     else:
         dt = get_build_datetime()
-    return int(dt.timestamp())
+    return max(int(dt.timestamp()), 0)
 
 
 def get_build_datetime() -> datetime: