configure: fixed OpenGL build when lavc not present

Do not add dependency/build hwaccel_libav_common.o if libavcodec is not
present as a dependency for OpenGL display.

configure.ac

@@ -1798,6 +1798,8 @@ then
         ADD_MODULE("vcompress_libavcodec", "$LIBAVCODEC_COMPRESS_OBJ", "$LIBAVCODEC_LIBS $LIBSWSCALE_LIBS")
         ADD_MODULE("vdecompress_libavcodec", "$LIBAVCODEC_DECOMPRESS_OBJ", "$LIBAVCODEC_LIBS $LAVC_HWACC_LIBS")
         ADD_MODULE("acompress_libavcodec", "$LIBAVCODEC_AUDIO_CODEC_OBJ", "$LIBAVCODEC_LIBS")
+else
+        HW_ACC_OBJ=
 fi
 
 if test $libavcodec_req = yes -a $libavcodec = no; then