Add missing lua_pop in luaGetFromRegistry (#11097)

This pr mainly has the following four changes:

1. Add missing lua_pop in `luaGetFromRegistry`.
    This bug affects `redis.register_function`, where `luaGetFromRegistry` in
    `luaRegisterFunction` will return null when we call `redis.register_function` nested.
    .e.g
    ```
    FUNCTION LOAD "#!lua name=mylib \n local lib=redis \n lib.register_function('f2', function(keys, args) lib.register_function('f1', function () end) end)"
    fcall f2 0
    ````
    But since we exit when luaGetFromRegistry returns null, it does not cause the stack to grow indefinitely.

3. When getting `REGISTRY_RUN_CTX_NAME` from the registry, use `serverAssert`
    instead of error return. Since none of these lua functions are registered at the time
    of function load, scriptRunCtx will never be NULL.
4. Add `serverAssert` for `luaLdbLineHook`, `luaEngineLoadHook`.
5. Remove `luaGetFromRegistry` from `redis_math_random` and
    `redis_math_randomseed`, it looks like they are redundant.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/eval.c b/src/eval.c
index e2ee41cb5..dd488a984 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -1629,6 +1629,7 @@ ldbLog(sdsnew("                     next line of code."));
  * to start executing a new line. */
 void luaLdbLineHook(lua_State *lua, lua_Debug *ar) {
     scriptRunCtx* rctx = luaGetFromRegistry(lua, REGISTRY_RUN_CTX_NAME);
+    serverAssert(rctx); /* Only supported inside script invocation */
     lua_getstack(lua,0,ar);
     lua_getinfo(lua,"Sl",ar);
     ldb.currentline = ar->currentline;