Add a check for checking if more than one input file is provided to

ffplay, make it complain and abort in that case as just one input file
is currently supported.

Originally committed as revision 22139 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffplay.c

@@ -2671,6 +2671,11 @@ static void show_help(void)
 
 static void opt_input_file(const char *filename)
 {
+    if (input_filename) {
+        fprintf(stderr, "Argument '%s' provided as input filename, but '%s' was already specified.\n",
+                filename, input_filename);
+        exit(1);
+    }
     if (!strcmp(filename, "-"))
         filename = "pipe:";
     input_filename = filename;