patch 8.2.3175: Vim9: using illegal pointer with nested lambdas.

Problem:    Vim9: using illegal pointer with inline function inside a lambda.
Solution:   Clear eval_tofree_cmdline when advancing to the next line.
            (closes #8578)

src/eval.c

@@ -2177,6 +2177,11 @@ eval_next_line(evalarg_T *evalarg)
 	vim_free(evalarg->eval_tofree);
 	evalarg->eval_tofree = line;
     }
+
+    // Advanced to the next line, "arg" no longer points into the previous
+    // line.
+    VIM_CLEAR(evalarg->eval_tofree_cmdline);
+
     return skipwhite(line);
 }