Return 0 for the size_t return type.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@153930 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/source/API/SBStream.cpp b/source/API/SBStream.cpp
index b08726f..dc8eb05 100644
--- a/source/API/SBStream.cpp
+++ b/source/API/SBStream.cpp
@@ -51,7 +51,7 @@
 SBStream::GetSize()
 {
     if (m_is_file || m_opaque_ap.get() == NULL)
-        return NULL;
+        return 0;
     
     return static_cast<StreamString *>(m_opaque_ap.get())->GetSize();
 }