Xpress: fix NLP results processing for Xpress 9.2.0

[jsiirola]

Fixes # .

Summary/Motivation:

Xpress 9.2.0 appears to return infeasible status differently than previous versions. In previous versions, infeasible nonlinear problems solved using the Xpress optimizer returned solution status via LPSTATUS. Beginning in 9.2, it appears that the problem status is now returned in XSLP_NLPSTATUS. This PR updates the results processor to only fall back on the LP results processor if LPRESULTS is nonzero (and XSLP_NLPSTATUS is 0)

@djunglas, am I interpreting the change in Xpress behavior correctly?

Changes proposed in this PR:

• Update processing of NLP results to only use the LP results processor if there the NLP results status is not set.

Legal Acknowledgement

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1. I agree my contributions are submitted under the BSD license.
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[mrmundt]

Typo!!

[mrmundt]

Please remind me later to change this error message. Because it's entirely not helpful.

[codecov]

Codecov Report

Patch coverage: 53.33% and project coverage change: +0.01% 🎉

Comparison is base (228f5eb) 87.81% compared to head (fcac472) 87.83%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2921      +/-   ##
==========================================
+ Coverage   87.81%   87.83%   +0.01%     
==========================================
  Files         770      770              
  Lines       89644    89645       +1     
==========================================
+ Hits        78721    78736      +15     
+ Misses      10923    10909      -14     

Flag	Coverage Δ
linux	84.86% <53.33%> (+<0.01%)	⬆️
osx	74.58% <53.33%> (+<0.01%)	⬆️
other	85.03% <53.33%> (+<0.01%)	⬆️
win	82.12% <53.33%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
pyomo/solvers/plugins/solvers/xpress_direct.py	72.71% <53.33%> (+0.95%)	⬆️

... and 2 files with indirect coverage changes

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