Do not add type alias templates twice to the AST

This also fixes a memory leak since the copies were never destroyed.

Signed-off-by: Dimitar Dobrev <dpldobrev@protonmail.com>

src/CppParser/Parser.cpp

@@ -1539,11 +1539,11 @@ TypeAliasTemplate* Parser::WalkTypeAliasTemplate(
     HandleDeclaration(TD, TA);
 
     TA->name = GetDeclName(TD);
+    NS->Templates.push_back(TA);
+
     TA->TemplatedDecl = WalkDeclaration(TD->getTemplatedDecl());
     TA->Parameters = WalkTemplateParameterList(TD->getTemplateParameters());
 
-    NS->Templates.push_back(TA);
-
     return TA;
 }