Clear array pointer after deallocation

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@44380 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/raster/history.c

@@ -310,6 +310,7 @@ void Rast_clear_history(struct History *hist)
     if (hist->lines)
 	G_free(hist->lines);
 
+    hist->lines = NULL;
     hist->nlines = 0;
 }