Use the file opened from argv[1] in preparser-process.cc

preparser/preparser-process.cc

Index: preparser/preparser-process.cc
diff --git a/preparser/preparser-process.cc b/preparser/preparser-process.cc
index 3a83a0a852fa19ceb8be78b553f6ea6912aad06f..26dfc42b53a89256759343e84fcb81bc586bdad3 100644
--- a/preparser/preparser-process.cc
+++ b/preparser/preparser-process.cc
@@ -193,8 +193,8 @@ int main(int argc, char* argv[]) {
   FILE* input = stdin;
   if (argc > 1) {
     char* arg = argv[1];
-    FILE* file = fopen(arg, "rb");
-    if (!file) return EXIT_FAILURE;
+    input = fopen(arg, "rb");
+    if (input == NULL) return EXIT_FAILURE;
   }
   int status = 0;
   do {