Make mythcommflag terminate early on 0-byte files

I had a rash of 0-byte files the other day, and I found that mythcommflag
would sit and spin trying to create some initial buffers, or something along
those lines.  This change makes it check if the file is 0 bytes.  If it is,
it will immediately quit with an error, rather than indefinitely try to
grind on it.

This may need some tweaking to deal with commflagging while recording as it
could cause a race condition if the file has no data at the moment that
mythcommflag starts.

mythtv/programs/mythcommflag/main.cpp

@@ -752,6 +752,15 @@ static int FlagCommercials(
 
     QString filename = get_filename(program_info);
 
+    QFile file(filename);
+    if (file.size() == 0)
+    {
+        VERBOSE(VB_IMPORTANT, QString("File %1 is zero-byte, aborting.")
+                .arg(filename));
+        global_program_info = NULL;
+        return GENERIC_EXIT_PERMISSIONS_ERROR;
+    }
+
     RingBuffer *tmprbuf = RingBuffer::Create(filename, false);
     if (!tmprbuf)
     {