fix topcrasher bug 252289, r=mvl sr=darin

netwerk/base/src/nsFileStreams.cpp

@@ -499,6 +499,8 @@ NS_IMETHODIMP
 nsSafeFileOutputStream::Init(nsIFile* file, PRInt32 ioFlags, PRInt32 perm,
                              PRInt32 behaviorFlags)
 {
+    NS_ENSURE_ARG(file);
+
     nsresult rv = file->Exists(&mTargetFileExists);
     if (NS_FAILED(rv)) {
         NS_ERROR("Can't tell if target file exists");

netwerk/base/src/nsFileStreams.h

@@ -162,6 +162,7 @@ public:
     NS_DECL_NSISAFEOUTPUTSTREAM
 
     nsSafeFileOutputStream() :
+        mTargetFileExists(PR_TRUE),
         mWriteResult(NS_OK) {}
 
     virtual ~nsSafeFileOutputStream() { nsSafeFileOutputStream::Close(); }

netwerk/cookie/src/nsCookieService.cpp

@@ -1034,6 +1034,10 @@ nsCookieService::Write()
     return NS_OK;
   }
 
+  if (!mCookieFile) {
+    return NS_ERROR_NULL_POINTER;
+  }
+
   nsresult rv;
   nsCOMPtr<nsIOutputStream> fileOutputStream;
   rv = NS_NewSafeLocalFileOutputStream(getter_AddRefs(fileOutputStream),