Fix handling of empty json diff

Dependencies

• [2] YUVLBWV3 Populate resource groups for unrecorded and untracked changes
• [3] ZGMIJNFV Create pijul.ts for executing commands using the Pijul CLI

Change contents

• edit in src/pijul.ts at line 207
  [2.2772]→[2.2772:2879](∅→∅)
  − const pijulDiff = JSON.parse((await this.pijul.exec(this.repositoryRoot, ['diff', '--json'])).stdout);
• replacement in src/pijul.ts at line 208
  [2.2915]→[2.2915:3001](∅→∅)
  − for (const file in pijulDiff) {

  − changedFiles.push(createResourceUri(file));
  [2.2915]

  [2.3001]
  + const output = (await this.pijul.exec(this.repositoryRoot, ['diff', '--json'])).stdout;

  + if (output !== '') {

  + const pijulDiff = JSON.parse(output);

  + for (const file in pijulDiff) {

  + changedFiles.push(createResourceUri(file));

  + }