layers: Fix doc validation file list check

The check for required files was counting the files multiple times and
aborting silently.  The check now correct counts files and exits with
non-zero exit code on failure.

Change-Id: I5b158f7cca0dd541571d95c00c3450139daf32c4
diff --git a/scripts/vk_validation_stats.py b/scripts/vk_validation_stats.py
index 0ec5797..af84c59 100755
--- a/scripts/vk_validation_stats.py
+++ b/scripts/vk_validation_stats.py
@@ -192,12 +192,12 @@
                     filepath = '../%s/layers/%s' % (build_dir, source)
                     if os.path.isfile(filepath):
                         qualified_paths.append(filepath)
-                        continue
+                        break
             if len(self.generated_source_files) != len(qualified_paths):
                 print("Error: Unable to locate one or more of the following source files in the %s directories" % (", ".join(generated_source_directories)))
                 print(self.generated_source_files)
                 print("Skipping documentation validation test")
-                quit()
+                exit(1)
             else:
                 self.source_files.extend(qualified_paths)