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/CodeGen/CGStmt.cpp b/lib/CodeGen/CGStmt.cpp
index 7f73c88..da586b1 100644
--- a/lib/CodeGen/CGStmt.cpp
+++ b/lib/CodeGen/CGStmt.cpp
@@ -801,7 +801,7 @@
   for (unsigned i = 0, e = S.getNumInputs(); i != e; i++) {
     TargetInfo::ConstraintInfo Info(S.getInputConstraint(i),
                                     S.getInputName(i));
-    bool result = Target.validateInputConstraint(&OutputConstraintInfos[0],
+    bool result = Target.validateInputConstraint(OutputConstraintInfos.data(),
                                                  S.getNumOutputs(),
                                                  Info); result=result;
     assert(result && "Failed to parse input constraint");