[llvm-dwarfdump] - Fix array out of bounds access crash.

This fixes possible out of bound access in
DWARFDie::getFirstChild()
which might happen when .debug_info section is corrupted,
like shown in testcase.

Differential revision: https://reviews.llvm.org/D39185

llvm-svn: 316566
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp b/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
index a534d36..d20eabf 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
@@ -511,6 +511,12 @@
   return DWARFDie();
 }
 
+DWARFDie DWARFDie::getFirstChild() const {
+  if (isValid())
+    return U->getFirstChild(Die);
+  return DWARFDie();
+}
+
 iterator_range<DWARFDie::attribute_iterator> DWARFDie::attributes() const {
   return make_range(attribute_iterator(*this, false),
                     attribute_iterator(*this, true));