fix: handle edge case when unable to parse usage code block

---
type: pre_commit_static_analysis_report
description: Results of running static analysis checks when committing changes.
report:
  - task: lint_filenames
    status: passed
  - task: lint_editorconfig
    status: passed
  - task: lint_markdown
    status: na
  - task: lint_package_json
    status: na
  - task: lint_repl_help
    status: na
  - task: lint_javascript_src
    status: passed
  - task: lint_javascript_cli
    status: na
  - task: lint_javascript_examples
    status: na
  - task: lint_javascript_tests
    status: na
  - task: lint_javascript_benchmarks
    status: na
  - task: lint_python
    status: na
  - task: lint_r
    status: na
  - task: lint_c_src
    status: na
  - task: lint_c_examples
    status: na
  - task: lint_c_benchmarks
    status: na
  - task: lint_c_tests_fixtures
    status: na
  - task: lint_shell
    status: na
  - task: lint_typescript_declarations
    status: passed
  - task: lint_typescript_tests
    status: na
  - task: lint_license_headers
    status: passed
---

Author: kgryte

lib/node_modules/@stdlib/_tools/markdown/namespace-toc/lib/toc.js

@@ -98,7 +98,12 @@ function createTOC( contents, aliases, blacklist ) {
 		descr = RE_DESCR.exec( str )[ 1 ];
 		descr = replace( descr, RE_LINKS, '$1' );
 		descr = uncapitalizeDescription( descr );
-		pkg = str.match( RE_PKG )[ 1 ];
+		pkg = str.match( RE_PKG );
+		if ( pkg === null ) {
+			debug( 'Unable to process file: %s. Skipping...', contents[ i ].file );
+			continue;
+		}
+		pkg = pkg[ 1 ];
 		pkgs.push( pkg );
 		debug( 'Processing package %s...', pkg );
 		multiple = str.match( RE_FUN );