Rev-parse: better error handling for chaining.

Fixed an error where "nonexistant^N" or similar
would fall into an assert. This now properly returns
an error. 

src/revparse.c

@@ -564,7 +564,10 @@ int git_revparse_single(git_object **out, git_repository *repo, const char *spec
 
          if (current_state != next_state && next_state != REVPARSE_STATE_DONE) {
             /* Leaving INIT state, find the object specified, in case that state needs it */
-            revparse_lookup_object(&next_obj, repo, git_buf_cstr(&specbuffer));
+            if (revparse_lookup_object(&next_obj, repo, git_buf_cstr(&specbuffer)) < 0) {
+               retcode = GIT_ERROR;
+               next_state = REVPARSE_STATE_DONE;
+            }
          }
          break;
 

tests-clar/refs/revparse.c

@@ -36,6 +36,8 @@ void test_refs_revparse__cleanup(void)
 void test_refs_revparse__nonexistant_object(void)
 {
    cl_git_fail(git_revparse_single(&g_obj, g_repo, "this doesn't exist"));
+   cl_git_fail(git_revparse_single(&g_obj, g_repo, "this doesn't exist^1"));
+   cl_git_fail(git_revparse_single(&g_obj, g_repo, "this doesn't exist~2"));
 }
 
 void test_refs_revparse__shas(void)