Fix T41617: Color ramp crashes user preferences

Color ramps with no handles caused issues.

source/blender/blenkernel/intern/texture.c

@@ -512,19 +512,18 @@ CBData *colorband_element_add(struct ColorBand *coba, float position)
 	if (coba->tot == MAXCOLORBAND) {
 		return NULL;
 	}
-	else if (coba->tot > 0) {
+	else {
 		CBData *xnew;
-		float col[4];
-
-		do_colorband(coba, position, col);
 
 		xnew = &coba->data[coba->tot];
 		xnew->pos = position;
 
-		xnew->r = col[0];
-		xnew->g = col[1];
-		xnew->b = col[2];
-		xnew->a = col[3];
+		if (coba->tot != 0) {
+			do_colorband(coba, position, &xnew->r);
+		}
+		else {
+			zero_v4(&xnew->r);
+		}
 	}
 
 	coba->tot++;

source/blender/editors/interface/interface_draw.c

@@ -1151,9 +1151,11 @@ void ui_draw_but_COLORBAND(uiBut *but, uiWidgetColors *UNUSED(wcol), const rcti
 	}
 
 	/* layer: active handle */
-	cbd = &coba->data[coba->cur];
-	pos = x1 + cbd->pos * (sizex - 1) + 1;
-	ui_draw_colorband_handle(rect, pos, &cbd->r, display, true);
+	if (coba->tot != 0) {
+		cbd = &coba->data[coba->cur];
+		pos = x1 + cbd->pos * (sizex - 1) + 1;
+		ui_draw_colorband_handle(rect, pos, &cbd->r, display, true);
+	}
 }
 
 void ui_draw_but_NORMAL(uiBut *but, uiWidgetColors *wcol, const rcti *rect)

source/blender/editors/interface/interface_handlers.c

@@ -5020,6 +5020,9 @@ static bool ui_numedit_but_COLORBAND(uiBut *but, uiHandleButtonData *data, int m
 	if (data->draglastx == mx)
 		return changed;
 
+	if (data->coba->tot == 0)
+		return changed;
+
 	dx = ((float)(mx - data->draglastx)) / BLI_rctf_size_x(&but->rect);
 	data->dragcbd->pos += dx;
 	CLAMP(data->dragcbd->pos, 0.0f, 1.0f);