Cortex deploy panic when object and prefix present on bucket

[RobertLucian]

Description

Assuming there's a path model/path/1 as specified in the API spec (predictor.models field), if there are objects with the model/path/1/ prefix and there's also an object strictly named model/path/1, then the following panic is thrown:

runtime.boundsError: runtime error: index out of range [6] with length 6
  File "/go/src/github.com/cortexlabs/cortex/pkg/lib/errors/error.go", line 78, in Wrap
  File "/go/src/github.com/cortexlabs/cortex/pkg/lib/errors/error.go", line 193, in CastRecoverError
  File "/go/src/github.com/cortexlabs/cortex/pkg/operator/endpoints/respond.go", line 76, in recoverAndRespond
  File "/go/src/github.com/cortexlabs/cortex/pkg/types/spec/utils.go", line 465, in determineBaseModelStructure
  File "/go/src/github.com/cortexlabs/cortex/pkg/types/spec/utils.go", line 290, in validateModels
  File "/go/src/github.com/cortexlabs/cortex/pkg/types/spec/validations.go", line 1200, in validateTensorFlowPredictor
  File "/go/src/github.com/cortexlabs/cortex/pkg/types/spec/validations.go", line 911, in validatePredictor
  File "/go/src/github.com/cortexlabs/cortex/pkg/types/spec/validations.go", line 811, in ValidateAPI
  File "/go/src/github.com/cortexlabs/cortex/pkg/operator/resources/validations.go", line 96, in ValidateClusterAPIs
  File "/go/src/github.com/cortexlabs/cortex/pkg/operator/resources/resources.go", line 106, in Deploy
  File "/go/src/github.com/cortexlabs/cortex/pkg/operator/endpoints/deploy.go", line 51, in Deploy
  File "/usr/local/go/src/net/http/server.go", line 2041, in HandlerFunc.ServeHTTP
  File "/go/src/github.com/cortexlabs/cortex/pkg/operator/endpoints/middleware.go", line 110, in AuthMiddleware.func1
  File "/usr/local/go/src/net/http/server.go", line 2041, in HandlerFunc.ServeHTTP
  File "/go/src/github.com/cortexlabs/cortex/pkg/operator/endpoints/middleware.go", line 131, in APIVersionCheckMiddleware.func1
  File "/usr/local/go/src/net/http/server.go", line 2041, in HandlerFunc.ServeHTTP
  File "/go/src/github.com/cortexlabs/cortex/pkg/operator/endpoints/middleware.go", line 60, in ClientIDMiddleware.func1
  File "/usr/local/go/src/net/http/server.go", line 2041, in HandlerFunc.ServeHTTP
  File "/go/src/github.com/cortexlabs/cortex/pkg/operator/endpoints/middleware.go", line 44, in PanicMiddleware.func1
  File "/usr/local/go/src/net/http/server.go", line 2041, in HandlerFunc.ServeHTTP
  File "/go/pkg/mod/github.com/gorilla/mux@v1.8.0/mux.go", line 210, in (*Router).ServeHTTP
  File "/usr/local/go/src/net/http/server.go", line 2836, in serverHandler.ServeHTTP
  File "/usr/local/go/src/net/http/server.go", line 1924, in (*conn).serve

As reported by @htahir1.