Don't do async keys command when client cannot block (#564)

Fixes #562

src/db.cpp

@@ -1059,7 +1059,7 @@ void keysCommand(client *c) {
     sds pattern = szFromObj(c->argv[1]);
 
     const redisDbPersistentDataSnapshot *snapshot = nullptr;
-    if (!(c->flags & (CLIENT_MULTI | CLIENT_BLOCKED)))
+    if (!(c->flags & (CLIENT_MULTI | CLIENT_BLOCKED | CLIENT_DENY_BLOCKING)))
         snapshot = c->db->createSnapshot(c->mvccCheckpoint, true /* fOptional */);
     if (snapshot != nullptr)
     {

tests/unit/scripting.tcl

@@ -43,6 +43,10 @@ start_server {tags {"scripting"}} {
         r eval {return redis.call('get',KEYS[1])} 1 mykey
     } {myval}
 
+    test { EVAL - keys command works? } {
+        r eval {return redis.call('keys', 'test')} 0
+    }
+
     test {EVALSHA - Can we call a SHA1 if already defined?} {
         r evalsha fd758d1589d044dd850a6f05d52f2eefd27f033f 1 mykey
     } {myval}