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/filepath.c b/src/filepath.c
index 1fe757e..6644e99 100644
--- a/src/filepath.c
+++ b/src/filepath.c
@@ -3083,7 +3083,7 @@
 
 #ifdef FEAT_EVAL
     if (*cmd == '=')	    // `={expr}`: Expand expression
-	buffer = eval_to_string(cmd + 1, &p, TRUE);
+	buffer = eval_to_string(cmd + 1, TRUE);
     else
 #endif
 	buffer = get_cmd_output(cmd, NULL,