Meta: Make test_pdf.py not count regular "failed to open" as crash

Some files just aren't valid PDF files that e.g. Preview.app can't
open either. Let's not count those (exit code 1) as crashes.

Meta/test_pdf.py

@@ -59,12 +59,17 @@ def main():
 
     results = multiprocessing.Pool().map(test_pdf, files)
 
+    failed_files = []
     num_crashes = 0
     stack_to_files = {}
     for r in results:
         print(r.filename)
         print(r.stdout.decode('utf-8'))
-        if r.returncode != 0:
+        if r.returncode == 0:
+            continue
+        if r.returncode == 1:
+            failed_files.append(r.filename)
+        else:
             num_crashes += 1
             stack_to_files.setdefault(r.stderr, []).append(r.filename)
 
@@ -83,6 +88,12 @@ def main():
     print(f'{num_crashes} crashes ({percent:.1f}%)')
     print(f'{len(keys)} distinct crash stacks')
 
+    percent = 100 * len(failed_files) / len(results)
+    print()
+    print(f'{len(failed_files)} failed to open ({percent:.1f}%)')
+    for f in failed_files:
+        print(f'    {f}')
+
 
 if __name__ == '__main__':
     main()