fix(wstaking): block region moves with delegations

[jamilahmadzai]

Summary

Fixes #1230.

This blocks UpdateValidator region reassignment when the old region still has active delegated funds. The current flow calls UnBondRegion(oldRegionId), which clears the old region operator before users in that region can safely undelegate, delegate again, or withdraw rewards. Rejecting the reassignment while DelegateAmount is non-zero keeps the old region state intact and avoids locking those delegations behind an empty operator address.

A reassignment with no delegated funds still follows the existing path and binds the validator to the new empty region.

Tests

• go test ./x/wstaking/keeper -run 'TestKeeperTestSuite/TestUpdateValidator(RejectsRegionMoveWithDelegations|MovesRegionWithoutDelegations)$' -count=1 -v
• go test ./x/wstaking/keeper -count=1
• go test ./x/wstaking/... -count=1
• git diff --check

Bounty payout

Meta Earth bug bounty payout in $MEC via ME Pass: me1ya82w6cjflk9r2qeyfeu64sm7gxtfr7mu62w9j