Well, reading the docs never hurts:
https://docs.particle.io/datasheets/photon-shields/#temperature-sensor-1-
https://docs.particle.io/datasheets/photon-datasheet/#power
The datasheet isn't a bad place to look either: https://datasheets.maximintegrated.com/en/ds/DS18B20.pdf (page 19).
Or pretty much any google search for "DS18B20 current consumption" would've gotten you there 
tl;rd: 4mA
From the pin description in the docs, we can gather the following:
VIN: This pin can be used as an input or output. As an input, supply 3.6 to 5.5VDC to power the Photon. When the Photon is powered via the USB port, this pin will output a voltage of approximately 4.8VDC due to a reverse polarity protection series schottky diode between VUSB and VIN. When used as an output, the max load on VIN is 1A.
tl;dr: 1A
12*4=48mA. 48<1000, so yeah, you should be good.
Info on the pins can be found here: https://docs.particle.io/datasheets/photon-datasheet/#peripherals-and-gpio
Happy Hack... ehm... Holidays 
Mini-guide for free: Photon Maker Kit Feedback - #6 by Moors7