Guard in USRGenerator::GenLoc() against null Decl* from invalid code.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@130541 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/libclang/CIndexUSRs.cpp b/tools/libclang/CIndexUSRs.cpp
index 68871e9..9917d2a 100644
--- a/tools/libclang/CIndexUSRs.cpp
+++ b/tools/libclang/CIndexUSRs.cpp
@@ -470,6 +470,12 @@
   if (generatedLoc)
     return IgnoreResults;
   generatedLoc = true;
+  
+  // Guard against null declarations in invalid code.
+  if (!D) {
+    IgnoreResults = true;
+    return true;
+  }
 
   const SourceManager &SM = AU->getSourceManager();
   SourceLocation L = D->getLocStart();