Return null pointer instead of 'false' (fixes clang warning).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@106755 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Checker/StreamChecker.cpp b/lib/Checker/StreamChecker.cpp
index 98d6993..c527ca2 100644
--- a/lib/Checker/StreamChecker.cpp
+++ b/lib/Checker/StreamChecker.cpp
@@ -267,7 +267,7 @@
                                     CheckerContext &C) {
   const DefinedSVal *DV = dyn_cast<DefinedSVal>(&SV);
   if (!DV)
-    return false;
+    return 0;
 
   ConstraintManager &CM = C.getConstraintManager();
   const GRState *stateNotNull, *stateNull;