fix: not showing empty context line below diff

For diffs with context around hunks (eg. using git diff -U1),
if the context line below a diff was empty then the line was not
shown, this commit fixes it.

src/utils/parse.ts

@@ -94,7 +94,7 @@ function normalizeDiffText(text: string) {
 }
 
 export function parseDiff(text: string, options: ParseOptions = {}): File[] {
- const diffText = normalizeDiffText(text.trim());
+ const diffText = normalizeDiffText(text.trimStart());
  const files = parser.parse(diffText);
 
  return files.map(file => mapFile(file, options));