Fix cluster redirect for module command with no firstkey. (#7539)
Fix cluster redirect for module command with no firstkey. (#7539)

Before this commit, processCommand() did not notice that cmd could be a module command
which declared `getkeys-api` and handled it for the purpose of cluster redirect it
as if it doesn't use any keys.

This commit fixed it by reusing the codes in addReplyCommand().
JackieXie168/redis,JackieXie168/redis,JackieXie168/redis,JackieXie168/redis