Add regression test for ocaml#4861

As in this commit, there should be no output captured from the
opam env --revert invocation.

tests/reftests/env.win32.test

@@ -1,6 +1,28 @@
 N0REP0
 ### : setenv & build env rewriting :
 ### opam switch create rewriting --empty
+### : Test for #4861
+### <pkg:multipath.1>
+opam-version: "2.0"
+setenv: [
+  [ PATH += "XXX:\\" ]
+  [ PATH += "C:\\Devel\\bin1;C:\\Devel\\bin2;\"C:\\Devel\\bin3;\";ZZZ:\\;C:\\Devel\\bin4" ]
+]
+x-env-path-rewrite: [
+  [ PATH false ]
+]
+### opam install multipath -yv | sed-cmd sh | unordered
+The following actions will be performed:
+=== install 1 package
+<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
+-> installed multipath.1
+Done.
+  - install multipath 1
+
+### opam env --shell=cmd | grep "PATH" | 'XXX:.*' -> ''
+set "MANPATH=:"${BASEDIR}/OPAM/rewriting/man""
+set "PATH=${BASEDIR}/OPAM/rewriting/bin;C:\Devel\bin1;C:\Devel\bin2;"C:\Devel\bin3;";ZZZ:\;C:\Devel\bin4;
+### opam exec -- opam env --shell=cmd --revert | grep 'ZZZ:'
 ### : Test for #5838
 ### opam env | grep MANPATH
 MANPATH=':"${BASEDIR}/OPAM/rewriting/man"'; export MANPATH;
@@ -595,6 +617,7 @@ x-env-path-rewrite: [
   [ RF_ENVSET_WITH_COL false ]
   [ RF_ENVSET_ADD false ]
   [ RF_ENVSET_ADD_WITH_COL false ]
+  [ PATH false ]
 
   [ RF_ENVBUILD false ]
   [ RF_ENVBUILD_STR false ]