Fix conversion from a bool value to a pointer.

Change-Id: I7e634ac08b6a54586ed2a335095515619ef1614d
diff --git a/lib/ExecutionEngine/MCCacheReader.cpp b/lib/ExecutionEngine/MCCacheReader.cpp
index 8404027..0a97abb 100644
--- a/lib/ExecutionEngine/MCCacheReader.cpp
+++ b/lib/ExecutionEngine/MCCacheReader.cpp
@@ -57,7 +57,7 @@
                                            Script *S) {
   // Check file handle
   if (!objFile || objFile->getFD() < 0 || !infoFile || infoFile->getFD() < 0) {
-    return false;
+    return NULL;
   }
 
   mObjFile = objFile;