If using debug-without-src policy then usr/src/debug won't exist,
therefore the function will fail due to missing files, adding a check
for files to exist before editing them fixes it.
(From OE-Core rev: 0eb85a2670c9250350b66647f4cbdae446be830f)
Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>