revparse: Free left side of invalid range revspecs

This fixes a small memory leak in git_revparse where early returns on
errors from git_revparse_single cause a free() on the (reallocated) left
side of the revspec to be skipped.

src/revparse.c

@@ -912,13 +912,9 @@ int git_revparse(
 			rstr++;
 		}
 
-		if ((error = git_revparse_single(&revspec->from, repo, lstr)) < 0) {
-			return error;
-		}
-
-		if ((error = git_revparse_single(&revspec->to, repo, rstr)) < 0) {
-			return error;
-		}
+		error = git_revparse_single(&revspec->from, repo, lstr);
+		if (error == 0)
+			error = git_revparse_single(&revspec->to, repo, rstr);
 
 		git__free((void*)lstr);
 	} else {