proj_alter_id(): make it replace an existing ID instead of appending a new one

Author: rouault

src/iso19111/common.cpp

@@ -761,6 +761,7 @@ void IdentifiedObject::Private::setIdentifiers(
 
         pVal = properties.get(Identifier::CODE_KEY);
         if (pVal) {
+            identifiers.clear();
             identifiers.push_back(
                 Identifier::create(std::string(), properties));
         }

test/unit/test_c_api.cpp

@@ -3524,6 +3524,13 @@ TEST_F(CApi, proj_alter_id) {
 
     EXPECT_EQ(std::string(proj_get_id_auth_name(alteredObj, 0)), "auth");
     EXPECT_EQ(std::string(proj_get_id_code(alteredObj, 0)), "code");
+
+    auto alteredObj2 = proj_alter_id(m_ctxt, alteredObj, "auth2", "code2");
+    ObjectKeeper keeper_alteredObj2(alteredObj2);
+    ASSERT_NE(alteredObj2, nullptr);
+
+    EXPECT_EQ(std::string(proj_get_id_auth_name(alteredObj2, 0)), "auth2");
+    EXPECT_EQ(std::string(proj_get_id_code(alteredObj2, 0)), "code2");
 }
 
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