patch 8.1.2301: MS-Windows GUI: drawing error when background color changes

Problem:    MS-Windows GUI: drawing error when background color changes.
Solution:   Implement gui_mch_new_colors(). (Simon Sadler)

src/gui_w32.c

@@ -1282,7 +1282,18 @@ vim_WindowProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
     void
 gui_mch_new_colors(void)
 {
-    /* nothing to do? */
+    HBRUSH prevBrush;
+
+    s_brush = CreateSolidBrush(gui.back_pixel);
+#ifdef SetClassLongPtr
+    prevBrush = (HBRUSH)SetClassLongPtr(
+				s_hwnd, GCLP_HBRBACKGROUND, (LONG_PTR)s_brush);
+#else
+    prevBrush = (HBRUSH)SetClassLong(
+				   s_hwnd, GCL_HBRBACKGROUND, (long_u)s_brush);
+#endif
+    InvalidateRect(s_hwnd, NULL, TRUE);
+    DeleteObject(prevBrush);
 }
 
 /*

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2301,
 /**/
     2300,
 /**/