JS: fix NPE

Author: aibaars

javascript/extractor/src/com/semmle/js/extractor/AutoBuild.java

@@ -1234,7 +1234,8 @@ private void doExtract(FileExtractor extractor, Path file, ExtractorState state)
       ParseResultInfo loc = extractor.extract(f, state);
       if (!extractor.getConfig().isExterns() && (loc == null || loc.getLinesOfCode() != 0)) seenCode = true;
       if (!extractor.getConfig().isExterns()) seenFiles = true;
-      for (ParseError err : loc.getParseErrors()) {
+      List<ParseError> errors = loc == null ? Collections.emptyList() : loc.getParseErrors();
+      for (ParseError err : errors) {
         String msg = "A parse error occurred: " + StringUtil.escapeMarkdown(err.getMessage())
             + ". Check the syntax of the file. If the file is invalid, correct the error or [exclude](https://docs.github.com/en/code-security/code-scanning/automatically-scanning-your-code-for-vulnerabilities-and-errors/customizing-code-scanning) the file from analysis.";
         // file, relative to the source root