patch 8.2.3648: "verbose pwd" is incorrect after dropping files on Vim

Problem:    "verbose pwd" is incorrect after dropping files on Vim.
Solution:   Set the chdir reason to "drop".

src/gui.c

@@ -5525,6 +5525,7 @@ gui_wingoto_xy(int x, int y)
 drop_callback(void *cookie)
 {
     char_u	*p = cookie;
+    int		do_shorten = FALSE;
 
     // If Shift held down, change to first file's directory.  If the first
     // item is a directory, change to that directory (and let the explorer
@@ -5534,11 +5535,16 @@ drop_callback(void *cookie)
 	if (mch_isdir(p))
 	{
 	    if (mch_chdir((char *)p) == 0)
-		shorten_fnames(TRUE);
+		do_shorten = TRUE;
 	}
 	else if (vim_chdirfile(p, "drop") == OK)
-	    shorten_fnames(TRUE);
+	    do_shorten = TRUE;
 	vim_free(p);
+	if (do_shorten)
+	{
+	    shorten_fnames(TRUE);
+	    last_chdir_reason = "drop";
+	}
     }
 
     // Update the screen display

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3648,
 /**/
     3647,
 /**/