patch 8.1.2073: when editing a buffer 'colorcolumn' may not work

Problem:    When editing a buffer 'colorcolumn' may not work.
Solution:   Set the buffer before copying option values. Call
            check_colorcolumn() after copying window options.

src/buffer.c

@@ -1738,22 +1738,22 @@ set_curbuf(buf_T *buf, int action)
     static void
 enter_buffer(buf_T *buf)
 {
-    /* Copy buffer and window local option values.  Not for a help buffer. */
+    // Get the buffer in the current window.
+    curwin->w_buffer = buf;
+    curbuf = buf;
+    ++curbuf->b_nwindows;
+
+    // Copy buffer and window local option values.  Not for a help buffer.
     buf_copy_options(buf, BCO_ENTER | BCO_NOHELP);
     if (!buf->b_help)
 	get_winopts(buf);
 #ifdef FEAT_FOLDING
     else
-	/* Remove all folds in the window. */
+	// Remove all folds in the window.
 	clearFolding(curwin);
-    foldUpdateAll(curwin);	/* update folds (later). */
+    foldUpdateAll(curwin);	// update folds (later).
 #endif
 
-    /* Get the buffer in the current window. */
-    curwin->w_buffer = buf;
-    curbuf = buf;
-    ++curbuf->b_nwindows;
-
 #ifdef FEAT_DIFF
     if (curwin->w_p_diff)
 	diff_buf_add(curbuf);
@@ -2980,9 +2980,7 @@ get_winopts(buf_T *buf)
     if (p_fdls >= 0)
 	curwin->w_p_fdl = p_fdls;
 #endif
-#ifdef FEAT_SYN_HL
-    check_colorcolumn(curwin);
-#endif
+    after_copy_winopt(curwin);
 }
 
 /*