light client cannot work when the number of validators is equal 100

[chengwenxi]

Tendermint version (use tendermint version or git rev-parse --verify HEAD if installed from source):

unreleased-master-b1646e51e263d579b4cc522668b4a2b81c1f56bd(v0.34.*)

What happened:

If the number of validators is equal 100(defined by maxPerPage), the light client cannot work.

How to reproduce it

• Option 1: Modify maxPerPage to 1 and run a network with one validator, https://github.com/chengwenxi/tendermint/tree/vincent-maxPerPage-1

  1. run a testnet network

     tendermint testnet --v 1
     tendermint node --home mytestnet/node0/ --proxy-app kvstore

  2. run a light client proxy server

     tendermint light chain-98I3B2 -p http://localhost:26657 --height 102 --hash 68778AD7342039B2DC46047B8221DAECCE0E2F663AEA16EFD51F94BF7A72DF26 -w http://localhost:26657

  It will be stuck for a long time and then return the following error:

  I[2021-01-29|16:16:45.341] Removing all light blocks                    
  I[2021-01-29|16:16:45.347] Downloading trusted light block using options 
  ERROR: client failed to respond. Tried to replace primary but: no witnesses connected. please reset light client
  

• Option 2: Use an existing network with 100 validators. The IRISnet bifrost testnet that based on tendermint@v0.34.1 and the validators has reached 100, we can access it by public node 34.80.22.255:26657.

  tendermint light bifrost-2 -p http://34.80.22.255:26657 --height 140150 --hash 0401E3281401DEFBFCCAF650B98A950282A7043AC5962331ECD02ADD8A2D56F5 -w http://34.80.22.255:26657

  It returns the same error as Option 1.

Why happened:

In function validatorSet,
we retry call p.client.Validators to get all validators by pages, if the len(validatorSet) = maxPerPage, p.client.Validators will return page should be within [1, {total_page}] range, ​{page}, see https://github.com/tendermint/tendermint/blob/master/rpc/core/env.go#L111.

Proposal

Minor fix: ignore this error in function validatorSet.