Fix crash

Author: JohnSully

src/db.cpp

@@ -3325,7 +3325,7 @@ void redisDbPersistentData::prefetchKeysAsync(client *c, parsed_command &command
     }
 }
 
-void redisDbPersistentData::prefetchKeysFlash(std::unordered_set<client*> &setc)
+void redisDbPersistentData::prefetchKeysFlash(const std::unordered_set<client*> &setc)
 {
     serverAssert(GlobalLocksAcquired());
     std::vector<sds> veckeys;
@@ -3334,6 +3334,8 @@ void redisDbPersistentData::prefetchKeysFlash(std::unordered_set<client*> &setc)
     for (client *c : setc) {
         for (auto &command : c->vecqueuedcmd) {
             getKeysResult result = GETKEYS_RESULT_INIT;
+            if (command.argc == 0)  // parse can do this it will be handled by processClient
+                break;
             auto cmd = lookupCommand(szFromObj(command.argv[0]));
             if (cmd == nullptr)
                 break; // Bad command? It's not for us to judge, just bail

src/server.h

@@ -1230,7 +1230,7 @@ class redisDbPersistentData
     bool keycacheIsEnabled();
 
     void prefetchKeysAsync(client *c, struct parsed_command &command);
-    void prefetchKeysFlash(std::unordered_set<client*> &setc);
+    void prefetchKeysFlash(const std::unordered_set<client*> &setc);
     void processStorageToken(StorageToken *tok);
 
     bool FSnapshot() const { return m_spdbSnapshotHOLDER != nullptr; }