Use assert for peel target type check

src/object.c

@@ -318,16 +318,11 @@ int git_object_peel(
 	if (git_object_type(object) == target_type)
 		return git_object_dup(peeled, (git_object *)object);
 
-	if (target_type != GIT_OBJ_TAG &&
-		target_type != GIT_OBJ_COMMIT &&
-		target_type != GIT_OBJ_TREE &&
-		target_type != GIT_OBJ_BLOB &&
-		target_type != GIT_OBJ_ANY) {
-
-		giterr_set(GITERR_OBJECT, "Cannot peel to object type %d",
-			(int)target_type);
-		return GIT_EINVALIDSPEC;
-	}
+	assert(target_type == GIT_OBJ_TAG ||
+		target_type == GIT_OBJ_COMMIT ||
+		target_type == GIT_OBJ_TREE ||
+		target_type == GIT_OBJ_BLOB ||
+		target_type == GIT_OBJ_ANY);
 
 	source = (git_object *)object;