git-p4: fix Git LFS pointer parsing

git-p4: fix Git LFS pointer parsing

Git LFS 1.2.0 removed a preamble from the output of the 'git lfs pointer'
command [1] which broke the parsing of this output. Adjust the parser
to support the old and the new format.

Please note that this patch slightly changes the second return parameter
from a list of LF terminated strings to a single string that contains
a number of LF characters.

[1] https://github.com/github/git-lfs/commit/da2935d9a739592bc775c98d8ef4df9c72ea3b43

Signed-off-by: Lars Schneider <redacted>
Helped-by: Sebastian Schuberth <redacted>
Helped-by: Ben Woosley <redacted>
Signed-off-by: Lars Schneider <redacted>
Signed-off-by: Junio C Hamano <redacted>