patch 8.2.1162: crash when using a lambda

Problem:    Crash when using a lambda.
Solution:   Check for evalarg to be NULL.
diff --git a/src/userfunc.c b/src/userfunc.c
index 6858068..2f253c9 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -508,7 +508,7 @@
     }
 
     eval_lavars_used = old_eval_lavars;
-    if (evalarg->eval_tofree == NULL)
+    if (evalarg != NULL && evalarg->eval_tofree == NULL)
 	evalarg->eval_tofree = tofree;
     else
 	vim_free(tofree);
@@ -519,7 +519,7 @@
     ga_clear_strings(&newlines);
     vim_free(fp);
     vim_free(pt);
-    if (evalarg->eval_tofree == NULL)
+    if (evalarg != NULL && evalarg->eval_tofree == NULL)
 	evalarg->eval_tofree = tofree;
     else
 	vim_free(tofree);