[libclang] Fix a crash with invalid code, while skip function bodies is enabled.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175860 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 189b3d9..03d18d4 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -8449,9 +8449,9 @@
 }
 
 Decl *Sema::ActOnSkippedFunctionBody(Decl *Decl) {
-  if (FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
+  if (FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(Decl))
     FD->setHasSkippedBody();
-  else if (ObjCMethodDecl *MD = dyn_cast<ObjCMethodDecl>(Decl))
+  else if (ObjCMethodDecl *MD = dyn_cast_or_null<ObjCMethodDecl>(Decl))
     MD->setHasSkippedBody();
   return ActOnFinishFunctionBody(Decl, 0);
 }