tests: resolve memleak in oxcmail_ie

CID 1559998: (#1 of 1): Resource leak (RESOURCE_LEAK)
6. leaked_storage: Variable mc going out of scope leaks the storage it points to.

tests/oxcmail_ie.cpp

@@ -13,6 +13,7 @@
 
 using namespace gromox;
 using namespace gi_dump;
+using mptr = std::unique_ptr<message_content, mc_delete>;
 
 static alloc_context g_alloc_mgr;
 
@@ -77,7 +78,7 @@ static int select_parts_1()
 	            appl_mixed_footer + appl_alt_footer;
 	MAIL m;
 	assert(m.load_from_str_move(data.data(), data.size()));
-	auto mc = oxcmail_import("us-ascii", "UTC", &m, g_alloc, ee_get_propids);
+	mptr mc(oxcmail_import("us-ascii", "UTC", &m, g_alloc, ee_get_propids));
 	assert(mc != nullptr);
 	auto atl = mc->children.pattachments;
 	assert(atl != nullptr);
@@ -104,7 +105,7 @@ static int select_parts_2()
 	            appl_html1 + appl_zip + appl_mixed_footer + appl_alt_footer;
 	MAIL m;
 	assert(m.load_from_str_move(data.data(), data.size()));
-	auto mc = oxcmail_import("us-ascii", "UTC", &m, g_alloc, ee_get_propids);
+	mptr mc(oxcmail_import("us-ascii", "UTC", &m, g_alloc, ee_get_propids));
 	assert(mc != nullptr);
 	auto atl = mc->children.pattachments;
 	assert(atl != nullptr);
@@ -166,7 +167,7 @@ static int select_parts_3()
 
 	MAIL m;
 	assert(m.load_from_str_move(data, std::size(data)));
-	auto mc = oxcmail_import("us-ascii", "UTC", &m, g_alloc, ee_get_propids);
+	mptr mc(oxcmail_import("us-ascii", "UTC", &m, g_alloc, ee_get_propids));
 	assert(mc != nullptr);
 	auto atl = mc->children.pattachments;
 	assert(atl != nullptr);