AVI demuxer: return AVERROR_EOF upon detection of end of file.

Originally committed as revision 17456 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/avidec.c

@@ -870,7 +870,7 @@ resync:
         }
     }
 
-    return -1;
+    return AVERROR_EOF;
 }
 
 /* XXX: We make the implicit supposition that the positions are sorted