patch 8.2.1902: default option values changed with :badd for existing buffer

Problem:    Default option values are changed when using :badd for an existing
            buffer.
Solution:   When calling buflist_new() pass a zero line number. (closes #7195)
diff --git a/src/ex_cmds.c b/src/ex_cmds.c
index 82e9c57..a9be36a 100644
--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -2630,7 +2630,9 @@
 	{
 	    if (flags & ECMD_ADDBUF)
 	    {
-		linenr_T	tlnum = 1L;
+		// Default the line number to zero to avoid that a wininfo item
+		// is added for the current window.
+		linenr_T	tlnum = 0;
 
 		if (command != NULL)
 		{