provider/aws: Guard clause to prevent panic on ELB connectionSettings

[stack72]

Fixes: #11705

% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSELB_'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/03/14 16:40:20 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSELB_ -timeout 120m
=== RUN   TestAccAWSELB_importBasic
--- PASS: TestAccAWSELB_importBasic (73.93s)
=== RUN   TestAccAWSELB_basic
--- PASS: TestAccAWSELB_basic (69.20s)
=== RUN   TestAccAWSELB_fullCharacterRange
--- PASS: TestAccAWSELB_fullCharacterRange (63.68s)
=== RUN   TestAccAWSELB_AccessLogs_enabled
--- PASS: TestAccAWSELB_AccessLogs_enabled (196.25s)
=== RUN   TestAccAWSELB_AccessLogs_disabled
--- PASS: TestAccAWSELB_AccessLogs_disabled (190.90s)
=== RUN   TestAccAWSELB_generatedName
--- PASS: TestAccAWSELB_generatedName (52.09s)
=== RUN   TestAccAWSELB_availabilityZones
--- PASS: TestAccAWSELB_availabilityZones (93.53s)
=== RUN   TestAccAWSELB_tags
--- PASS: TestAccAWSELB_tags (102.96s)
=== RUN   TestAccAWSELB_iam_server_cert
--- PASS: TestAccAWSELB_iam_server_cert (70.91s)
=== RUN   TestAccAWSELB_swap_subnets
--- PASS: TestAccAWSELB_swap_subnets (261.42s)
=== RUN   TestAccAWSELB_InstanceAttaching
--- PASS: TestAccAWSELB_InstanceAttaching (196.82s)
=== RUN   TestAccAWSELB_HealthCheck
--- PASS: TestAccAWSELB_HealthCheck (60.64s)
=== RUN   TestAccAWSELB_Timeout
--- PASS: TestAccAWSELB_Timeout (62.71s)
=== RUN   TestAccAWSELB_ConnectionDraining
--- PASS: TestAccAWSELB_ConnectionDraining (58.25s)
=== RUN   TestAccAWSELB_SecurityGroups
--- PASS: TestAccAWSELB_SecurityGroups (153.64s)
PASS
ok  	github.com/hashicorp/terraform/builtin/providers/aws	1706.980s

[tombuildsstuff]

LGTM

[ghost]

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