[5pt] index 0 is out of bounds for axis 0 with size 0

[RobHanna-NOAA]

Found in a test run PR: v4.5.0.0 bug fixes #1150 . branch: dev-fix-alaska-bridges

Finalize catchments and model streams 19020602 0
Adjusting model reach rating curves
To Node 21281 cannot calculate max stream order for no upstream segments; multiple downstream segments scenario. Exception 
 KeyError('order_') 

Traceback (most recent call last):
  File "/foss_fim/src/add_crosswalk.py", line 483, in <module>
    add_crosswalk(**args)
  File "/foss_fim/src/add_crosswalk.py", line 250, in add_crosswalk
    update_id = output_flows.loc[
IndexError: index 0 is out of bounds for axis 0 with size 0

Found in 5 of 12040101's branches. This was a small batch test with 5 other hucs completing just fine.