Fix Obj2yaml bug and add comment where the iterator starts uninitialized!

Author: Jlalond

llvm/include/llvm/Object/Minidump.h

@@ -140,6 +140,11 @@ class MinidumpFile : public Binary {
     size_t Stride;
   };
 
+
+  /// Class the provides an iterator over the memory64 memory ranges. Ranges
+  /// are not validated before hand, and so any increment operation could fail.
+  /// For this reason, the iterator in it's initial state points to a default
+  /// initialized std::pair and should be advanced before dereferencing.
   class Memory64Iterator {
   public:
     static Memory64Iterator

llvm/lib/ObjectYAML/MinidumpYAML.cpp

@@ -539,9 +539,11 @@ Stream::create(const Directory &StreamDesc, const object::MinidumpFile &File) {
     if (!ExpectedList)
       return ExpectedList.takeError();
     std::vector<Memory64ListStream::entry_type> Ranges;
-    for (auto It = ExpectedList->begin(); It != ExpectedList->end(); ++It) {
+    for (auto It = ExpectedList->begin(); It != ExpectedList->end();) {
+      // Explicilty advance the iterator before dereference.
+      ++It;
       const auto Pair = *It;
-      if (Err.success()) {
+      if (!Err) {
         Ranges.push_back({Pair.first, Pair.second});
       }
     }