Fix AST walking default-case in switch-statement

[SupunS]

Description

Default-case's doesn't have an expression, skip it from visiting.

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• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[codecov-commenter]

Codecov Report

Merging #1433 (bcdbf86) into master (de9ccd9) will increase coverage by 0.00%.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master    #1433   +/-   ##
=======================================
  Coverage   73.12%   73.12%           
=======================================
  Files         283      283           
  Lines       39081    39082    +1     
=======================================
+ Hits        28577    28578    +1     
  Misses       9056     9056           
  Partials     1448     1448           

Flag	Coverage Δ
unittests	73.12% <0.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
runtime/ast/statement.go	92.64% <0.00%> (-0.35%)	⬇️
runtime/sema/simple_type.go	96.42% <0.00%> (+3.57%)	⬆️

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[github-actions]

Cadence Benchstat comparison

This branch with compared with the base branch onflow:master commit de9ccd9
The command for i in {1..N}; do go test ./... -run=XXX -bench=. -shuffle=on; done was used.
Bench tests were run a total of 7 times on each branch.

Results

	old.txt	new.txt
	time/op		delta
RuntimeFungibleTokenTransfer-2	1.50ms ±25%	1.70ms ± 4%	~	(p=0.073 n=7+6)
RuntimeResourceDictionaryValues-2	16.8ms ± 3%	16.6ms ± 3%	~	(p=0.456 n=7+7)
ParseFungibleToken-2	222µs ± 2%	224µs ± 7%	~	(p=0.535 n=7+7)
ParseArray-2	17.9ms ± 2%	17.9ms ± 6%	~	(p=0.628 n=6+7)
ParseInfix-2	10.3µs ± 6%	10.0µs ± 2%	~	(p=0.366 n=7+6)
ParseDeploy/byte_array-2	29.1ms ± 6%	29.5ms ± 2%	~	(p=0.731 n=7+6)
ParseDeploy/decode_hex-2	1.44ms ± 3%	1.41ms ± 3%	~	(p=0.101 n=7+6)
QualifiedIdentifierCreation/One_level-2	2.84ns ± 2%	2.84ns ± 2%	~	(p=0.805 n=7+7)
QualifiedIdentifierCreation/Three_levels-2	169ns ± 2%	168ns ± 1%	~	(p=0.250 n=7+7)
ContractInterfaceFungibleToken-2	47.9µs ± 2%	47.9µs ± 2%	~	(p=1.000 n=7+7)
CheckContractInterfaceFungibleTokenConformance-2	158µs ± 2%	157µs ± 2%	~	(p=0.731 n=7+6)
InterpretRecursionFib-2	2.84ms ± 4%	2.78ms ± 4%	~	(p=0.165 n=7+7)
NewInterpreter/new_interpreter-2	1.30µs ± 2%	1.33µs ± 8%	~	(p=0.805 n=7+7)
NewInterpreter/new_sub-interpreter-2	2.57µs ± 2%	2.63µs ± 5%	~	(p=0.165 n=7+7)
	alloc/op		delta
RuntimeFungibleTokenTransfer-2	282kB ± 0%	282kB ± 0%	~	(p=0.456 n=7+7)
RuntimeResourceDictionaryValues-2	4.05MB ± 0%	4.05MB ± 0%	~	(p=0.383 n=7+7)
QualifiedIdentifierCreation/One_level-2	0.00B	0.00B	~	(all equal)
QualifiedIdentifierCreation/Three_levels-2	64.0B ± 0%	64.0B ± 0%	~	(all equal)
ContractInterfaceFungibleToken-2	26.6kB ± 0%	26.6kB ± 0%	~	(p=0.245 n=7+6)
CheckContractInterfaceFungibleTokenConformance-2	66.2kB ± 0%	66.2kB ± 0%	~	(p=0.538 n=7+6)
InterpretRecursionFib-2	1.24MB ± 0%	1.24MB ± 0%	~	(p=0.462 n=7+7)
NewInterpreter/new_interpreter-2	768B ± 0%	768B ± 0%	~	(all equal)
NewInterpreter/new_sub-interpreter-2	1.24kB ± 0%	1.24kB ± 0%	~	(all equal)
	allocs/op		delta
RuntimeFungibleTokenTransfer-2	4.54k ± 0%	4.54k ± 0%	~	(p=0.714 n=7+7)
RuntimeResourceDictionaryValues-2	102k ± 0%	102k ± 0%	~	(p=0.755 n=7+7)
QualifiedIdentifierCreation/One_level-2	0.00	0.00	~	(all equal)
QualifiedIdentifierCreation/Three_levels-2	2.00 ± 0%	2.00 ± 0%	~	(all equal)
ContractInterfaceFungibleToken-2	458 ± 0%	458 ± 0%	~	(all equal)
CheckContractInterfaceFungibleTokenConformance-2	1.07k ± 0%	1.07k ± 0%	~	(all equal)
InterpretRecursionFib-2	25.0k ± 0%	25.0k ± 0%	~	(all equal)
NewInterpreter/new_interpreter-2	12.0 ± 0%	12.0 ± 0%	~	(all equal)
NewInterpreter/new_sub-interpreter-2	38.0 ± 0%	38.0 ± 0%	~	(all equal)