Fix LCS behaviour when non existant keys are provided

[danielealbano]

This PR fixes the behaviour of the LCS command when non existant keys are provided and also handle errors. The PR also expand the tests done for the LCS command to better cover the possible cases.

[codecov[bot]]

Codecov Report

Merging #191 (a4cd156) into main (0b7dbe2) will increase coverage by 1.03%. The diff coverage is 83.59%.

@@            Coverage Diff             @@
##             main     #191      +/-   ##
==========================================
+ Coverage   78.88%   79.92%   +1.03%     
==========================================
  Files         107      115       +8     
  Lines        6947     7185     +238     
==========================================
+ Hits         5480     5742     +262     
+ Misses       1467     1443      -24     

Impacted Files	Coverage Δ
.../module/redis/command/module_redis_command_hello.c	69.86% <50.00%> (-1.57%)	:arrow_down:
...odule/redis/command/module_redis_command_flushdb.c	60.00% <60.00%> (ø)
...module/redis/command/module_redis_command_msetnx.c	80.49% <80.49%> (ø)
...c/module/redis/command/module_redis_command_pttl.c	81.82% <81.82%> (ø)
...rc/module/redis/command/module_redis_command_ttl.c	81.82% <81.82%> (ø)
...module/redis/command/module_redis_command_getset.c	82.61% <82.61%> (ø)
...rc/module/redis/command/module_redis_command_lcs.c	86.78% <86.78%> (ø)
...module/redis/command/module_redis_command_dbsize.c	100.00% <100.00%> (ø)
...rc/module/redis/command/module_redis_command_del.c	100.00% <100.00%> (+18.18%)	:arrow_up:
...module/redis/command/module_redis_command_exists.c	100.00% <100.00%> (ø)
... and 6 more

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