gn: Don't do an out-of-bound access if a file ends after 'else' BUG=640857 Review-Url: https://codereview.chromium.org/2282493002 Cr-Original-Commit-Position: refs/heads/master@{#414461} Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src Cr-Mirrored-Commit: 5aba5ce9d5f3184b1e659c319e962c57274cbe03