[region-isolation] Fix a nullptr error.

This is triggered by the test case in the next commit. The problem is anonymous
closures can be passed here and they do not have a ValueDecl so there isn't a
decl for us to use.

(cherry picked from commit 57392b1)

Author: gottesmm

lib/SILOptimizer/Mandatory/TransferNonSendable.cpp

@@ -110,7 +110,7 @@ getTransferringApplyCalleeInfo(SILInstruction *inst) {
     return {};
 
   auto *decl = declRef->getDecl();
-  if (!decl->hasName())
+  if (!decl || !decl->hasName())
     return {};
 
   return {{decl->getDescriptiveKind(), decl->getName()}};