Fix log dev load issue.

[sanebay]

Issue.
Getting asserts in logdev during recovery with mismatch in logdev idx and complaining header corrupted.

Cause
One of the logdev family 1 was not used for writes in UT and has no chunks. During recovery, when we read m_vdev_jd->sync_next_read(), we ignored the return value whether we read anything or not. On build machines, the return buffer contained garbage values, which later was considered as invalid header and end of log. log_stream_reader::next_group() line 58. For some reason on github actions, we get a proper loggroup header(from logdev family 0, because crc was matching with sequence number) as garbage value and causing it validate against a invalid header and doing a assert. This issue didnt happen before dynamic logdev changes because we had fixed number chunks for both logdev families and it read some junk and returned error with no more logdev data. Now we have situation of 0 chunks and no garbage data.

Fix
handle the return code m_vdev_jd->sync_next_read() and handle case where then is no data needs to be read.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ec25d4c) 62.18% compared to head (a0546d5) 60.89%.
Report is 2 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #299      +/-   ##
==========================================
- Coverage   62.18%   60.89%   -1.29%     
==========================================
  Files         137      109      -28     
  Lines       14022     9180    -4842     
  Branches     1693     1184     -509     
==========================================
- Hits         8719     5590    -3129     
+ Misses       4604     3061    -1543     
+ Partials      699      529     -170     

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