Fix aggregation definition error logs

[niveathika]

Purpose

$subject, fixes #1537

Security checks

• Followed secure coding standards in http://wso2.com/technical-reports/wso2-secure-engineering-guidelines? yes
• Ran FindSecurityBugs plugin and verified report? yes
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets? yes

[codecov-io]

Codecov Report

Merging #1538 into master will increase coverage by 0.02%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master    #1538      +/-   ##
============================================
+ Coverage     67.91%   67.93%   +0.02%     
  Complexity       45       45              
============================================
  Files           648      648              
  Lines         27313    27313              
  Branches       4296     4296              
============================================
+ Hits          18550    18556       +6     
+ Misses         6967     6962       -5     
+ Partials       1796     1795       -1

Impacted Files	Coverage Δ	Complexity Δ
.../io/siddhi/core/util/parser/AggregationParser.java	75.27% <0%> (ø)	0 <0> (ø)	⬇️
.../io/siddhi/core/util/snapshot/SnapshotService.java	71.63% <0%> (+1.24%)	0% <0%> (ø)	⬇️

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