patch 8.2.5146: memory leak when substitute expression nests

Problem:    Memory leak when substitute expression nests.
Solution:   Use an array of expression results.
diff --git a/src/alloc.c b/src/alloc.c
index 6d4db62..6e2a30a 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -586,6 +586,9 @@
 # ifdef FEAT_QUICKFIX
     check_quickfix_busy();
 # endif
+# ifdef FEAT_EVAL
+    free_resub_eval_result();
+# endif
 }
 #endif