patch 8.1.2085: MS-Windows: draw error moving cursor over double-cell char

Problem:    MS-Windows: draw error moving cursor over double-cell character.
Solution:   Move the cursor to the left edge if needed. (Nobuhiro Takasaki,
            closes #4986)

src/os_win32.c

@@ -5831,7 +5831,7 @@ delete_lines(unsigned cLines)
 
 
 /*
- * Set the cursor position
+ * Set the cursor position to (x,y) (1-based).
  */
     static void
 gotoxy(
@@ -5841,14 +5841,25 @@ gotoxy(
     if (x < 1 || x > (unsigned)Columns || y < 1 || y > (unsigned)Rows)
 	return;
 
-    /* external cursor coords are 1-based; internal are 0-based */
-    g_coord.X = x - 1;
-    g_coord.Y = y - 1;
-
     if (!USE_VTP)
+    {
+	// external cursor coords are 1-based; internal are 0-based
+	g_coord.X = x - 1;
+	g_coord.Y = y - 1;
 	SetConsoleCursorPosition(g_hConOut, g_coord);
+    }
     else
+    {
+	// Move the cursor to the left edge of the screen to prevent screen
+	// destruction.  Insider build bug.
+	if (conpty_type == 3)
+	    vtp_printf("\033[%d;%dH", g_coord.Y + 1, 1);
+
 	vtp_printf("\033[%d;%dH", y, x);
+
+	g_coord.X = x - 1;
+	g_coord.Y = y - 1;
+    }
 }
 
 
@@ -7266,7 +7277,7 @@ mch_setenv(char *var, char *value, int x UNUSED)
  * Confirm until this version.  Also the logic changes.
  * insider preview.
  */
-#define CONPTY_INSIDER_BUILD	    MAKE_VER(10, 0, 18898)
+#define CONPTY_INSIDER_BUILD	    MAKE_VER(10, 0, 18990)
 
 /*
  * Not stable now.

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2085,
 /**/
     2084,
 /**/