Wrong Error Message When Node Running on Older Version of Protocol

**Describe the bug**
Minor bug - I think we can improve our error message for this common mistake of trying to run the newest node on an older version of the protocol.

**To Reproduce**
Steps to reproduce the behavior:
1. Try to launch the CLI for a PM-compatible broadcasting node on the current Rinkeby contract.

**Screenshots**
```
+-----------+
|NODE STATS|
+-----------+
*-----------------------------*--------------------------------------------*
| HTTP Port | 7935 |
*-----------------------------*--------------------------------------------*
| Controller Address | 0x37dC71366Ec655093b9930bc816E16e6b587F968 |
*-----------------------------*--------------------------------------------*
| LivepeerToken Address | 0x24f56eF2fED379421BEE64Ecafc2bC744f72522b |
*-----------------------------*--------------------------------------------*
| LivepeerTokenFaucet Address | 0xD69A2eC8f2F83267CE82A6d01837045BaE0EB9Bc |
*-----------------------------*--------------------------------------------*
| ETH Account | 0xf73580a0D020870Fdc2B6bde65235F57acf39FCC |
*-----------------------------*--------------------------------------------*
| LPT Balance | 0 |
*-----------------------------*--------------------------------------------*
| ETH Balance | 0 |
*-----------------------------*--------------------------------------------*
+-----------------+
|BROADCASTER STATS|
+-----------------+
ERROR: logging before flag.Parse: E0117 15:50:00.077154 16559 wizard_stats.go:123] Error getting sender info: invalid character 'c' looking for beginning of value
^C
```

On B:
```
I0117 15:49:40.084376 16551 mediaserver.go:115] Transcode Job Price: 1, Transcode Job Type: [{P240p30fps16x9 600k 30 426x240 16:9} {P360p30fps16x9 1200k 30 640x360 16:9}]
I0117 15:49:40.084488 16551 lpms.go:97] HTTP Server listening on http://127.0.0.1:8935
I0117 15:49:40.084497 16551 lpms.go:90] LPMS Server listening on rtmp://127.0.0.1:1935
E0117 15:49:48.320920 16551 handlers.go:24] HTTP Response Error 500: could not query sender info: ErrNoResult
```

Reproduce the failure by launching the CLI against the current Rinkeby contract, then inspect wizard_stats.go:123 and the related error reported through handlers.go:24. Compare the node and protocol responses shown in the report. Done means the older-protocol case produces an actionable error message instead of the JSON parsing and ErrNoResult messages.

Written by the indexing model from the issue text.