Improve date indicator for next price drop

[LukSteib]

Goal

Don't show "In invalid date" any longer for the next price drop on the vault page

Context

For some collateral types (experienced during tests for USDC-A) we show "In invalid date" as an indicator for the next price dop.
We might approve that by indicating that the date is not available for these cases instead of cryptic invalid date that might confuse the user

Assets

USDC-A vault creation simulation

Tasks

• Adjust the information on next price drop with a more speaking information