patch 8.2.1049: Vim9: leaking memory when using continuation line

Problem:    Vim9: leaking memory when using continuation line.
Solution:   Keep a pointer to the continuation line in evalarg_T.  Centralize
            checking for a next command.
diff --git a/src/fold.c b/src/fold.c
index d91203c..043037f 100644
--- a/src/fold.c
+++ b/src/fold.c
@@ -1928,7 +1928,7 @@
 	    curbuf = wp->w_buffer;
 
 	    ++emsg_silent; // handle exceptions, but don't display errors
-	    text = eval_to_string_safe(wp->w_p_fdt, NULL,
+	    text = eval_to_string_safe(wp->w_p_fdt,
 			 was_set_insecurely((char_u *)"foldtext", OPT_LOCAL));
 	    --emsg_silent;