fix(staking): fix impossible conditions (backport #19621) (#19624)

Co-authored-by: Tom <54514587+GAtom22@users.noreply.github.com>
Co-authored-by: sontrinh16 <trinhleson2000@gmail.com>
Co-authored-by: Julien Robert <julien@rbrt.fr>

x/staking/keeper/delegation.go

@@ -850,7 +850,7 @@ func (k Keeper) Unbond(
 		}
 
 		valAddr, err1 := k.validatorAddressCodec.StringToBytes(delegation.GetValidatorAddr())
-		if err != nil {
+		if err1 != nil {
 			return amount, err1
 		}