find: match nothing when -mindepth exceeds -maxdepth

[Developer1010x]

Fixes #778.

Problem

$ mkdir -p /tmp/dt/a/b/c && touch /tmp/dt/a/b/c/f /tmp/dt/a/x

$ /usr/bin/find /tmp/dt -mindepth 3 -maxdepth 1     # GNU
$ find /tmp/dt -mindepth 3 -maxdepth 1              # uutils, before
/tmp/dt/a

An empty depth range should match nothing, but uutils printed entries at depth 1.

Cause

walkdir's min_depth() and max_depth() setters both clamp min_depth down to max_depth, so -mindepth 3 -maxdepth 1 was silently turned into -mindepth 1 -maxdepth 1. Swapping the call order does not help — either setter clamps.

Fix

Detect the impossible range before building the walker. In that case walk the starting point only (max_depth(0)), so errors for a bad starting point are still reported, and discard every entry the walk yields.

$ find /nope -mindepth 3 -maxdepth 1
Error: /nope: No such file or directory (os error 2)   # rc=1, matching GNU's diagnostic

Verification

Every combination below now agrees with GNU find on output and exit code, with and without -depth:

args	GNU	uutils
-mindepth 3 -maxdepth 1	(empty)	(empty)
-mindepth 5 -maxdepth 0	(empty)	(empty)
-mindepth 1 -maxdepth 3	4 entries	same
-mindepth 2 -maxdepth 2	2 entries	same
-maxdepth 1	2 entries	same
-mindepth 2	4 entries	same

Added find_mindepth_greater_than_maxdepth, covering both traversal orders. cargo test, cargo clippy --all-targets -- -D warnings and cargo fmt --check are all clean.

No GNU source was consulted; the fix is derived from walkdir's documented clamping behaviour.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.32%. Comparing base (3de01a0) to head (4401d05).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #854      +/-   ##
==========================================
+ Coverage   92.31%   92.32%   +0.01%     
==========================================
  Files          35       35              
  Lines        7466     7482      +16     
  Branches      388      391       +3     
==========================================
+ Hits         6892     6908      +16     
  Misses        433      433              
  Partials      141      141              

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[codspeed-hq]

Merging this PR will not alter performance

✅ 20 untouched benchmarks

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_{Comparing Developer1010x:find-mindepth-gt-maxdepth (4401d05) with main (3de01a0)}