Ensure that we do not pass a negative number to VS Code for error diagnostics

[orta]

Hello there, looks like if Flow gives an error with 0 as the line, this extension will not show results:

flow status --pretty packages/jest-editor-support/src/test_reconciler.js | pbcopy

{
  "flowVersion":"0.36.0",
  "errors":[
    {
      "kind":"internal",
      "level":"error",
      "message":[
        {
          "context":null,
          "descr":"Internal error: Failure(\"attempt to refine type TestReconcilationState\")\n",
          "type":"Blame",
          "loc":{
            "source":"/Users/orta/dev/projects/vscode/jest/packages/jest-editor-support/src/test_reconciler.js",
            "type":"SourceFile",
            "start":{"line":0,"column":1,"offset":0},
            "end":{"line":0,"column":0,"offset":0}
          },
          "path":"/Users/orta/dev/projects/vscode/jest/packages/jest-editor-support/src/test_reconciler.js",
          "line":0,
          "endline":0,
          "start":1,
          "end":0
        }
      ]
    },
    {
      ...

This fixes that 👍

[gabelevi]

Awesome! Thanks for the fix! This looks good to me!