Bug 541828 followup: Convert "sizeof" result to signed integer, to fix signed-vs-unsigned build warning in nsZipArchive. r=tglek

modules/libjar/nsZipArchive.cpp

@@ -538,7 +538,7 @@ nsresult nsZipArchive::BuildFileList()
 
   //-- Read the central directory headers
   buf = startp + centralOffset;
-  if (endp - buf < sizeof(PRUint32))
+  if (endp - buf < PRInt32(sizeof(PRUint32)))
       return NS_ERROR_FILE_CORRUPTED;
   PRUint32 sig = xtolong(buf);
   while (sig == CENTRALSIG) {