Update add event command to throw the correct exception

[LinkedInk]

Throws CommandException correctly instead of IndexOutOfBoundsException which causes the app to not respond. Closes #248

[codecov-io]

Codecov Report

Merging #247 into master will decrease coverage by 0.06%.
The diff coverage is 40.00%.

@@             Coverage Diff              @@
##             master     #247      +/-   ##
============================================
- Coverage     61.37%   61.31%   -0.07%     
  Complexity      923      923              
============================================
  Files           140      140              
  Lines          3350     3355       +5     
  Branches        396      397       +1     
============================================
+ Hits           2056     2057       +1     
- Misses         1117     1120       +3     
- Partials        177      178       +1     

Impacted Files	Coverage Δ	Complexity Δ
...address/logic/commands/events/AddEventCommand.java	52.77% <40.00%> (-2.45%)	10.00 <0.00> (ø)

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[solkim-83]

lgtm