fix a bad free crash

Author: jcupitt

TODO

@@ -1,3 +1,10 @@
+valgrind!
+
+==1537060== Conditional jump or move depends on uninitialised value(s)
+==1537060==    at 0x1978B5: drawstate_free (plotdisplay.c:183)
+==1537060==    by 0x198C01: plotdisplay_to_image (plotdisplay.c:573)
+==1537060==    by 0x14038D: apply_graph_export_image_call (builtin.c:521)
+
 # menu redesign
 
 - remove unused widgets

src/plotdisplay.c

@@ -274,6 +274,9 @@ drawstate_draw(Drawstate *state,
 static void
 drawstate_init(Drawstate *state)
 {
+	state->kccfg = NULL;
+	state->kplot = NULL;
+
 	// minimal config for thumbnail draw
 	kplotcfg_defaults(&state->kcfg_thumbnail);
 	state->kcfg_thumbnail.xinterval = 0;
@@ -293,8 +296,6 @@ drawstate_init(Drawstate *state)
 	state->kcfg_window.clrs = plotdisplay_series_ccfg;
 	state->kcfg_window.ticlabelfont = plotdisplay_tic_font;
 	state->kcfg_window.axislabelfont = plotdisplay_axis_font;
-
-	state->kplot = NULL;
 }
 
 static void