Use v.data() instead of &v[0] when SmallVector v might be empty.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@72210 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaType.cpp b/lib/Sema/SemaType.cpp
index 4889a56..e10a912 100644
--- a/lib/Sema/SemaType.cpp
+++ b/lib/Sema/SemaType.cpp
@@ -795,7 +795,7 @@
           
           ArgTys.push_back(ArgTy);
         }
-        T = Context.getFunctionType(T, &ArgTys[0], ArgTys.size(),
+        T = Context.getFunctionType(T, ArgTys.data(), ArgTys.size(),
                                     FTI.isVariadic, FTI.TypeQuals);
       }
       break;