refspec: return GIT_EINVALIDSPEC for invalid specs

Disambiguate invalid specifications in `git_refspec__parse` so that
callers can determine the difference between invalid specifications and
actual errors.  No call sites wil propagagte this new error message to
an end-user, so there is no user-facing API change.

src/refspec.c

@@ -155,9 +155,10 @@ int git_refspec__parse(git_refspec *refspec, const char *input, bool is_fetch)
 	return 0;
 
 invalid:
-        git_error_set(
-                GIT_ERROR_INVALID,
+	git_error_set(GIT_ERROR_INVALID,
 	              "'%s' is not a valid refspec.", input);
+	git_refspec__dispose(refspec);
+	return GIT_EINVALIDSPEC;
 
 on_error:
 	git_refspec__dispose(refspec);

src/remote.c

@@ -110,12 +110,8 @@ static int write_add_refspec(git_repository *repo, const char *name, const char
 	if ((error = ensure_remote_name_is_valid(name)) < 0)
 		return error;
 
-	if ((error = git_refspec__parse(&spec, refspec, fetch)) < 0) {
-		if (git_error_last()->klass != GIT_ERROR_NOMEMORY)
-			error = GIT_EINVALIDSPEC;
-
+	if ((error = git_refspec__parse(&spec, refspec, fetch)) < 0)
 		return error;
-	}
 
 	git_refspec__dispose(&spec);
 

tests/network/refspecs.c

@@ -13,7 +13,7 @@ static void assert_refspec(unsigned int direction, const char *input, bool is_ex
 	if (is_expected_to_be_valid)
 		cl_assert_equal_i(0, error);
 	else
-		cl_assert_equal_i(GIT_ERROR, error);
+		cl_assert_equal_i(GIT_EINVALIDSPEC, error);
 }
 
 void test_network_refspecs__parsing(void)