Issue Type: Bug

Writing a brace-initializer list for a std::map whose values are std::variant types will cause IntelliSense to crash and cease providing suggestions or error squiggles for the entire file containing the initializer list. Even after deleting the offending declaration, IntelliSense will not work for the file that used to contain it until VS Code is restarted.

Steps to reproduce the problem:

1. In VSCode with the C/C++ extension enabled, create a new cpp source file and enter the following code:

#include <map>
#include <variant>

struct Foo {
    int a;
};
struct Bar {
    int a;
    bool b;
};

int main(int argc, char** argv) {
    std::map<int, std::variant<Foo, Bar>> test = {
        {0, Foo{1}},
        {1, Bar{2, true}},
    };
    
    return 0;
}

2. On the blank line before "return 0", type test.

   Expected result: An IntelliSense pop-up menu appears showing member functions of std::map as potential completions.

   Actual result: Nothing happens.

3. Press enter, leaving the incomplete line of code test..

   Expected result: A red error squiggle underlines the invalid syntax.

   Actual result: Nothing happens.

Extension version: 0.28.1
VS Code version: Code 1.45.1 (5763d909d5f12fe19f215cbfdd29a91c0fa9208a, 2020-05-14T08:27:22.494Z)
OS version: Linux x64 4.15.0-100-generic snap