patch 8.1.1547: functionality of bt_nofile() is confusing

Problem:    Functionality of bt_nofile() is confusing.
Solution:   Split into bt_nofile() and bt_nofilename().
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 0ef7609..544426f 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -1943,7 +1943,7 @@
 		if (buf->b_fname != NULL
 			&& (path_with_url(buf->b_fname)
 #ifdef FEAT_QUICKFIX
-			    || bt_nofile(buf)
+			    || bt_nofilename(buf)
 #endif
 			   )
 			&& STRCMP(buf->b_fname, avar->vval.v_string) == 0)