Fix assertion on loading AOF with timed out script. (#8284)

If AOF file contains a long Lua script that timed out, then the `evalCommand` calls
`blockingOperationEnds` which sets `server.blocked_last_cron` to 0. later on,
the AOF `whileBlockedCron` function asserts that this value is not 0.

The fix allows nesting call to `blockingOperationStarts` and `blockingOperationEnds`.

The issue was first introduce in this commit: 9ef8d2f67 (Redis 6.2 RC1)

src/server.c

@@ -2187,12 +2187,16 @@ int serverCron(struct aeEventLoop *eventLoop, long long id, void *clientData) {
 
 
 void blockingOperationStarts() {
+    if(!server.blocking_op_nesting++){
         updateCachedTime(0);
         server.blocked_last_cron = server.mstime;
+    }
 }
 
 void blockingOperationEnds() {
+    if(!(--server.blocking_op_nesting)){
         server.blocked_last_cron = 0;
+    }
 }
 
 /* This function fill in the role of serverCron during RDB or AOF loading, and
@@ -3004,6 +3008,7 @@ void initServer(void) {
     server.events_processed_while_blocked = 0;
     server.system_memory_size = zmalloc_get_memory_size();
     server.blocked_last_cron = 0;
+    server.blocking_op_nesting = 0;
 
     if ((server.tls_port || server.tls_replication || server.tls_cluster)
                 && tlsConfigure(&server.tls_ctx_config) == C_ERR) {

src/server.h

@@ -1468,6 +1468,7 @@ struct redisServer {
     int daylight_active;        /* Currently in daylight saving time. */
     mstime_t mstime;            /* 'unixtime' in milliseconds. */
     ustime_t ustime;            /* 'unixtime' in microseconds. */
+    size_t blocking_op_nesting; /* Nesting level of blocking operation, used to reset blocked_last_cron. */
     long long blocked_last_cron; /* Indicate the mstime of the last time we did cron jobs from a blocking operation */
     /* Pubsub */
     dict *pubsub_channels;  /* Map channels to list of subscribed clients */