[clang] [clang][ExtractAPI] fix a couple crashes when used via libclang (PR #132297)

[via cfe-commits]

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@@ -0,0 +1,33 @@
+// Test is line- and column-sensitive. Run lines are below
+
+template <typename T>
+class basic_vector {
+public:
+    T x;
+    T y;
+};
+
+using my_vec = basic_vector<int>;
+
+class MyClass {
+    my_vec myVec;
+};
+
+struct OuterStruct {
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QuietMisdreavus wrote:

The null `bases` problem was showing up when generating a single-symbol symbol graph for a forward declaration. The second `c-index-test` call is probing for `InnerStruct`, which was previously crashing. It might not need to be declared within another type; that's just how i saw it in the wild.

https://github.com/llvm/llvm-project/pull/132297