Set seed min and max to match other nodes

[eric-swanson]

This matches other nodes that have a seed value, for example the KSampler at https://github.com/comfyanonymous/ComfyUI/blob/master/nodes.py#L1357

This fixes the seed getting stuck at max 2048 in increment mode, or always returning a value <= 2048 in randomize mode.

Repro steps:

• create a "Random Prompts" node
• set the seed value to 3000 and control_after_generate to increment
• Queue Prompt
• notice that the seed resets to 2048