DIFF command panics when definition property type changes from an array to a non-array type

[zmay2030]

Problem statement

When a definition property changes from array type to another non-array type, the swagger DIFF results in a panic.

Steps to reproduce

spec_1.json

{
  "swagger": "2.0",
  "info": {
    "title": "Swagger Fixture",
    "version": "1.0"
  },
  "paths": {
    "/a/": {
      "get": {
        "parameters": [
          {
            "name": "",
            "in": "body",
            "schema": { "$ref": "#/definitions/A1" }
          }
        ],
        "responses": {
          "200": {
            "description": "200 response",
            "schema": {
              "type": "array",
              "items": { "$ref": "#/definitions/A1" }
            }
          }
        }
      }
    }
  },
  "definitions": {
    "A1": {
      "type": "object",
      "properties": {
        "a": { "type": "array" }
      }
    }
  }
}

spec_2.json

{
  "swagger": "2.0",
  "info": {
    "title": "Swagger Fixture",
    "version": "1.0"
  },
  "paths": {
    "/a/": {
      "get": {
        "parameters": [
          {
            "name": "",
            "in": "body",
            "schema": { "$ref": "#/definitions/A1" }
          }
        ],
        "responses": {
          "200": {
            "description": "200 response",
            "schema": {
              "type": "array",
              "items": { "$ref": "#/definitions/A1" }
            }
          }
        }
      }
    }
  },
  "definitions": {
    "A1": {
      "type": "object",
      "properties": {
        "a": { "type": "object" }
      }
    }
  }
}

Then Run swagger diff spec_1.json spec_2.json.

It was result in a panic

goroutine 1 [running]:
github.com/go-swagger/go-swagger/cmd/swagger/commands/diff.getTypeFromSchemaProps(0x1400054e488)
        /projects/go-swagger/cmd/swagger/commands/diff/schema.go:50 +0x138
github.com/go-swagger/go-swagger/cmd/swagger/commands/diff.getSchemaType({0x10549a9e0?, 0x1400054e488?})
        /projects/go-swagger/cmd/swagger/commands/diff/schema.go:69 +0x108
github.com/go-swagger/go-swagger/cmd/swagger/commands/diff.fromSchemaProps(...)
        /projects/go-swagger/cmd/swagger/commands/diff/spec_analyser.go:489

Environment

swagger version: 2.0
go version: 1.18
OS: Mac Monterey