Throw IOE instead of NPE if OpenSSHKeyV1KeyFile reads an empty file

[vladimirlagunov]

There is a contract that FileKeyProvider.readKey throws an IOException if something goes wrong. Throwing an NPE is not expected by API users. Also, it is much more difficult to find out if the NPE is thrown due to a broken key file, or due to an internal bug.

[codecov-commenter]

Codecov Report

Merging #773 (1980072) into master (69812e9) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master     #773   +/-   ##
=========================================
  Coverage     64.45%   64.46%           
- Complexity     1460     1461    +1     
=========================================
  Files           211      211           
  Lines          8617     8619    +2     
  Branches        807      808    +1     
=========================================
+ Hits           5554     5556    +2     
- Misses         2640     2641    +1     
+ Partials        423      422    -1     

Impacted Files	Coverage Δ
...sshj/userauth/keyprovider/OpenSSHKeyV1KeyFile.java	84.66% <100.00%> (+1.55%)	⬆️
...t/schmizz/sshj/connection/ConnectionException.java	22.22% <0.00%> (-11.12%)	⬇️
...va/net/schmizz/sshj/connection/ConnectionImpl.java	56.09% <0.00%> (-3.26%)	⬇️
...main/java/net/schmizz/sshj/xfer/scp/SCPEngine.java	73.01% <0.00%> (-3.18%)	⬇️
...java/net/schmizz/sshj/transport/TransportImpl.java	66.80% <0.00%> (+1.65%)	⬆️
.../main/java/net/schmizz/sshj/sftp/PacketReader.java	95.74% <0.00%> (+4.25%)	⬆️

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[hierynomus]

Thanks for fixing the bug ;)