user-unfriendly error message from `query leadership-schedule`

*Internal*

**Area**
*Other* Any other topic (Delegation, Ranking, ...).

**Summary**
Running `cardano-cli query leadership-schedule` at a time in an epoch when stake distribution is unstable leads to error like

```
cardano-cli query leadership-schedule --genesis /scratch/cardano-node-tests/state-cluster0/shelley/genesis.json --vrf-signing-key-file /scratch/cardano-node-tests/state-cluster0/nodes/node-pool3/vrf.skey --cold-verification-key-file /scratch/cardano-node-tests/state-cluster0/nodes/node-pool3/cold.vkey --next --testnet-magic 42 --cardano-mode
```
> Command failed: query leadership-schedule Error: Error while calculating the slot range: PastHorizon {pastHorizonCallStack = [("runQuery",SrcLoc {srcLocPackage = "ouroboros-consensus-0.1.0.0-3WJNO431PEsEUwRPtCeeUr", srcLocModule = "Ouroboros.Consensus.HardFork.History.Qry", srcLocFile = "src/Ouroboros/Consensus/HardFork/History/Qry.hs", srcLocStartLine = 430, srcLocStartCol = 44, srcLocEndLine = 430, srcLocEndCol = 64}),("interpretQuery",SrcLoc {srcLocPackage = "ouroboros-consensus-0.1.0.0-3WJNO431PEsEUwRPtCeeUr", srcLocModule = "Ouroboros.Consensus.HardFork.History.EpochInfo", srcLocFile = "src/Ouroboros/Consensus/HardFork/History/EpochInfo.hs", srcLocStartLine = 45, srcLocStartCol = 50, srcLocEndLine = 45, srcLocEndCol = 68}),("interpretQuery'",SrcLoc {srcLocPackage = "ouroboros-consensus-0.1.0.0-3WJNO431PEsEUwRPtCeeUr", srcLocModule = "Ouroboros.Consensus.HardFork.History.EpochInfo", srcLocFile = "src/Ouroboros/Consensus/HardFork/History/EpochInfo.hs", srcLocStartLine = 34, srcLocStartCol = 31, srcLocEndLine = 34, srcLocEndCol = 63}),("epochInfoSize_",SrcLoc {srcLocPackage = "cardano-slotting-0.1.0.0-6VyoKllhKMr9HEkTJGSq3p", srcLocModule = "Cardano.Slotting.EpochInfo.API", srcLocFile = "src/Cardano/Slotting/EpochInfo/API.hs", srcLocStartLine = 45, srcLocStartCol = 9, srcLocEndLine = 45, srcLocEndCol = 23}),("epochInfoSize",SrcLoc {srcLocPackage = "cardano-slotting-0.1.0.0-6VyoKllhKMr9HEkTJGSq3p", srcLocModule = "Cardano.Slotting.EpochInfo.API", srcLocFile = "src/Cardano/Slotting/EpochInfo/API.hs", srcLocStartLine = 122, srcLocStartCol = 26, srcLocEndLine = 122, srcLocEndCol = 42}),("epochInfoSize_",SrcLoc {srcLocPackage = "cardano-slotting-0.1.0.0-6VyoKllhKMr9HEkTJGSq3p", srcLocModule = "Cardano.Slotting.EpochInfo.API", srcLocFile = "src/Cardano/Slotting/EpochInfo/API.hs", srcLocStartLine = 45, srcLocStartCol = 9, srcLocEndLine = 45, srcLocEndCol = 23}),("epochInfoSize",SrcLoc {srcLocPackage = "cardano-slotting-0.1.0.0-6VyoKllhKMr9HEkTJGSq3p", srcLocModule = "Cardano.Slotting.EpochInfo.API", srcLocFile = "src/Cardano/Slotting/EpochInfo/API.hs", srcLocStartLine = 78, srcLocStartCol = 9, srcLocEndLine = 78, srcLocEndCol = 40})], pastHorizonExpression = Some (EEpochSize (ELit (EpochNo 31))), pastHorizonSummary = [EraSummary {eraStart = Bound {boundTime = RelativeTime 0s, boundSlot = SlotNo 0, boundEpoch = EpochNo 0}, eraEnd = EraEnd (Bound {boundTime = RelativeTime 200s, boundSlot = SlotNo 100, boundEpoch = EpochNo 1}), eraParams = EraParams {eraEpochSize = EpochSize 100, eraSlotLength = SlotLength 2s, eraSafeZone = StandardSafeZone 20}},EraSummary {eraStart = Bound {boundTime = RelativeTime 200s, boundSlot = SlotNo 100, boundEpoch = EpochNo 1}, eraEnd = EraEnd (Bound {boundTime = RelativeTime 400s, boundSlot = SlotNo 1100, boundEpoch = EpochNo 2}), eraParams = EraParams {eraEpochSize = EpochSize 1000, eraSlotLength = SlotLength 0.2s, eraSafeZone = StandardSafeZone 300}},EraSummary {eraStart = Bound {boundTime = RelativeTime 400s, boundSlot = SlotNo 1100, boundEpoch = EpochNo 2}, eraEnd = EraEnd (Bound {boundTime = RelativeTime 600s, boundSlot = SlotNo 2100, boundEpoch = EpochNo 3}), eraParams = EraParams {eraEpochSize = EpochSize 1000, eraSlotLength = SlotLength 0.2s, eraSafeZone = StandardSafeZone 300}},EraSummary {eraStart = Bound {boundTime = RelativeTime 600s, boundSlot = SlotNo 2100, boundEpoch = EpochNo 3}, eraEnd = EraEnd (Bound {boundTime = RelativeTime 800s, boundSlot = SlotNo 3100, boundEpoch = EpochNo 4}), eraParams = EraParams {eraEpochSize = EpochSize 1000, eraSlotLength = SlotLength 0.2s, eraSafeZone = StandardSafeZone 300}},EraSummary {eraStart = Bound {boundTime = RelativeTime 800s, boundSlot = SlotNo 3100, boundEpoch = EpochNo 4}, eraEnd = EraEnd (Bound {boundTime = RelativeTime 6200s, boundSlot = SlotNo 30100, boundEpoch = EpochNo 31}), eraParams = EraParams {eraEpochSize = EpochSize 1000, eraSlotLength = SlotLength 0.2s, eraSafeZone = StandardSafeZone 300}}]}

In previous node release the error message contained string "current stake distribution is currently unstable" which is more indicative of what is the actual problem.

**System info (please complete the following information):**
- OS Name: Fedora 35
- Node version: latest master (2b2d5dd4e2c349c6075f8abb338bce1911d09fe0)