App launcher: Fix warning log on unresolvable relative paths.

In the current implementation, the helper function DoMakePathAbsolute
may rewrite the input even in the case of failure,
which makes the warning log less readable.

BUG=none
TEST=./chrome --app --app-id=someapp --enable-logging=stderr non/existing/path

Review URL: https://codereview.chromium.org/665053002

Cr-Commit-Position: refs/heads/master@{#300424}
1 file changed