Taking 0 to the power of any negative exponent equals infinity. In Max, this yields the unique float value inf. In cases where you want to avoid getting inf, and would prefer to get 0, you can simply make a special case for a 0 input, and pass it on directly, avoiding the pow object. On the left is an example of how to use routepass to force Max to output 0 when it would otherwise calculate infinity, such as when using a pow -1 object.
The way audio Max compiles audio signal networks is, whenever audio is turned on, MSP outlets send out the message ‘signal’. (In other words, that’s how Max knows how MSP objects are connected to each other, and thus knows how to calculate the audio signal network.) The [route signal] object detects the selector ‘signal’ and sends a ‘bang’ out its left outlet in response. The [t signal] object converts that ‘bang’ back into the message ‘signal’.