Fix 32-bit wrap in refresh_pattern min/max values.

Fix 32-bit wrap in refresh_pattern min/max values.

Attached patch limits the values to 1 year (arbitrary based on rumours
about good caching times). Checking for 32-bit wrap and setting the max
1 year limit instead of cutting them to zero.

The expected outcome of this is correct cache storage time extension
according to refresh_pattern documentation when people desperately set
min/max to > a million minutes. Instead of a silent always-stale verdict.