BUG: Fix RecursionError when using a scalar point to select IntervalIndex columns

[jschendel]

• closes RecursionError when selecting single column from IntervalIndex #26490
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[codecov]

Codecov Report

Merging #26570 into master will decrease coverage by 50.08%.
The diff coverage is 0%.

@@             Coverage Diff             @@
##           master   #26570       +/-   ##
===========================================
- Coverage   91.77%   41.68%   -50.09%     
===========================================
  Files         174      174               
  Lines       50681    50681               
===========================================
- Hits        46513    21127    -25386     
- Misses       4168    29554    +25386

Flag	Coverage Δ
#multiple	?
#single	41.68% <0%> (-0.07%)	⬇️

Impacted Files	Coverage Δ
pandas/core/frame.py	34.99% <0%> (-62.13%)	⬇️
pandas/io/formats/latex.py	0% <0%> (-100%)	⬇️
pandas/io/sas/sas_constants.py	0% <0%> (-100%)	⬇️
pandas/core/groupby/categorical.py	0% <0%> (-100%)	⬇️
pandas/tseries/plotting.py	0% <0%> (-100%)	⬇️
pandas/tseries/converter.py	0% <0%> (-100%)	⬇️
pandas/io/formats/html.py	0% <0%> (-99.37%)	⬇️
pandas/io/sas/sas7bdat.py	0% <0%> (-91.16%)	⬇️
pandas/io/sas/sas_xport.py	0% <0%> (-90.1%)	⬇️
pandas/core/tools/numeric.py	10.14% <0%> (-89.86%)	⬇️
... and 129 more

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[codecov]

Codecov Report

Merging #26570 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #26570      +/-   ##
==========================================
- Coverage   91.77%   91.76%   -0.01%     
==========================================
  Files         174      174              
  Lines       50681    50683       +2     
==========================================
- Hits        46513    46511       -2     
- Misses       4168     4172       +4

Flag	Coverage Δ
#multiple	90.3% <100%> (ø)	⬆️
#single	41.66% <0%> (-0.09%)	⬇️

Impacted Files	Coverage Δ
pandas/core/frame.py	97% <100%> (-0.12%)	⬇️
pandas/io/gbq.py	78.94% <0%> (-10.53%)	⬇️

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[jreback]

rather would not inject specific index logic here

you can make this not a single key (so it takes a different branch)

or define one of the _convert_to_index routines which dispatch to the index type

[jreback]

@jschendel can you merge master and had some comments

[jbrockmendel]

@jschendel can you rebase

[jschendel]

I don't have a cleaner implementation here, and will need to come back to this later. Closing for now as I don't want this sitting around stale.