Fix NSIndexPathSyntheticFrontEnd::Impl::Clear() to only clear the active union member

[shafik]

Summary

NSIndexPathSyntheticFrontEnd::Impl::Clear() currently calls Clear() on both unions members regardless of which one is active. I modified it to only call Clear() on the active member.

[shafik]

I believe that NSIndexPathSyntheticFrontEnd::Update() also needs a fix in order to properly set the active member but I will do that as a separate fix since.

[JDevlieghere]

LGTM

lldb/source/Plugins/Language/ObjC/NSIndexPath.cpp

struct Impl {
     };
 
     union {
       struct InlinedIndexes m_inlined;
       struct OutsourcedIndexes m_outsourced;
     };
 
     void Clear() {
-      m_mode = Mode::Invalid;
+      switch (m_mode) {
+      case Mode::Inlined:
         m_inlined.Clear();
+        break;
+      case Mode::Outsourced:
         m_outsourced.Clear();
+        break;
+      case Mode::Invalid:
+        break;
+      }
+      m_mode = Mode::Invalid;
     }
 
     Impl() {}
 
     Mode m_mode = Mode::Invalid;
   } m_impl;
 
   uint32_t m_ptr_size = 0;