Don't try to (un)compress GDAL-linked maps

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@49681 15284696-431f-4ddb-bdfa-cd5b030d7da7

raster/r.compress/main.c

@@ -113,6 +113,10 @@ static int process(char *name, int uncompress)
 		  name, rname, rmapset);
 	return 1;
     }
+    if (G_find_file2_misc("cell_misc", "gdal", name, G_mapset())) {
+	G_warning(_("[%s] is a GDAL-linked map - can't (un)compress"), name);
+	return 1;
+    }
 
     map_type = Rast_map_type(name, G_mapset());