[analyzer] Fix crash in body farm for getter without implicit self.

Fix a crash in body farm when synthesizing a getter for a property
synthesized for a property declared in a protocol on a class extension
that shadows a declaration of the property in a category.

In this case, Sema doesn't fill in the implicit 'self' parameter for the getter
in the category, which leads to a crash when trying to synthesize the getter
for it.

To avoid the crash, skip getter synthesis in body farm if the self parameter is
not filled int.

rdar://problem/29938138

llvm-svn: 291635
diff --git a/clang/lib/Analysis/BodyFarm.cpp b/clang/lib/Analysis/BodyFarm.cpp
index d202a04..56c812c 100644
--- a/clang/lib/Analysis/BodyFarm.cpp
+++ b/clang/lib/Analysis/BodyFarm.cpp
@@ -467,6 +467,8 @@
   ASTMaker M(Ctx);
 
   const VarDecl *selfVar = Prop->getGetterMethodDecl()->getSelfDecl();
+  if (!selfVar)
+    return nullptr;
 
   Expr *loadedIVar =
     M.makeObjCIvarRef(