Hey!
I'm sorry but currently there is not a feature that prevents the use of spaces :(
I know that is just a random suggestion but you can try to solve the problem in a design way like guiding your player in searching for keywords that are not separated by spaces. Or better you can use a trick but you have to be good with the organization of conditional branches.
Using the "Script" section of conditional branches you can check the variable used for registering player's inputs this way:
$gameVariables.value(variableId).contains(" ")
This way you'll check if the prompt of the player contains at least a space. If it happens you can like retrieve a "system message" (a simple show text or what you want considering your game) that warns the player that "Spaces are not allowed!"
Good luck!