Confusing error message when EXT-OUTFLOW is used as the observation type in SFT

[rbwinst-usgs]

Describe the bug
When EXT-OUTFLOW is used in the SFT package in a reach that has downstream reaches, the error message generated by MODFLOW is confusing. (MODFLOW 6 version 6.3 runs normally if the observation is in the most downstream reach.) This was also tested on the nightly build downloaded on Aug. 24, 2022. In the nightly release version, the error also occurs if the observation is in the most downstream reach instead of reach 8. In Modflow 6.3, the error report is slightly different. It has

1. EXT-OUTFLOW must be > 0 or <= 0. (specified value is 8).
   The following error report is for the nightly release.
   ERROR REPORT:

2. EXT-OUTFLOW must be > 0 or <= -36844083. (specified value is 8).

UNIT ERROR REPORT:

1. ERROR OCCURRED WHILE READING FILE
   'C:\ModelingTools\ModelMuse\PracticeModels\SftObs\SftObs.Chem.ob_sfr'

To Reproduce
Run the attached model

Expected behavior
provide a useful error message

Screenshots
none

Desktop (please complete the following information):

• OS: Windows
• Version 10
  SftObs.zip

[rbwinst-usgs]

Using TO-MVR in SFT gives the same sort of error.