worktree: fix resource leaks when branch creation fails

worktree: fix resource leaks when branch creation fails

In the "add" subcommand, when `run_command()` fails while creating a new
branch (line 948), the function returns -1 immediately without freeing
the allocations made earlier: path (from prefix_filename at line 858),
opt_track, branch_to_free, and new_branch_to_free.

Redirect the error return through the existing cleanup block at the end
of the function so all four allocations are properly freed.

Pointed out by Coverity.

Assisted-by: Claude Opus 4.6
Signed-off-by: Johannes Schindelin <redacted>
Signed-off-by: Junio C Hamano <redacted>