Backport of "datetime: Return G_MAXFLOAT instead of G_MAXDOUBLE for no timezone offset" into 1.22
Backport of !4264 (merged) "datetime: Return G_MAXFLOAT instead of G_MAXDOUBLE for no timezone offset".
Commits:
- 49c9f318 datetime: Return G_MAXFLOAT instead of G_MAXDOUBLE for no timezone offset