branch: do capture the error code

We want to ignore GIT_ENOTFOUND, but for that we need to capture the
error code from the reflog deletion.

src/branch.c

@@ -138,7 +138,7 @@ int git_branch_delete(git_reference *branch)
 	if (git_reference_delete(branch) < 0)
 		goto on_error;
 
-	if (git_reflog_delete(git_reference_owner(branch), git_reference_name(branch)) < 0) {
+	if ((error = git_reflog_delete(git_reference_owner(branch), git_reference_name(branch))) < 0) {
 		if (error == GIT_ENOTFOUND) {
 			giterr_clear();
 			error = 0;