Fixed crash happening due to schema does not exist during GRANT operation

[Deepesh125]

Previously, If end user tries to grant select on table using schema qualified name and if schema does not exist then server will crash due to segmentation fault issue. This commit aims to fix that issue by appropriately checking existence of the schema.

Task: BABEL-5078

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[coveralls]

Pull Request Test Coverage Report for Build 9763377548

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 73.419%

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Totals
Change from base Build 9741962184:	0.0%
Covered Lines:	42164
Relevant Lines:	57429

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💛 - Coveralls