FindMatlab: Fix logic error when minimum version is not found

Fix logic added by commit 7fdd5128b1 (FindMatlab: Fix version selection
if a version is given, 2021-07-02, v3.22.0-rc1~66^2).  Ensure that
`_list_index` is always initialized to -1, akin to `list(FIND)` not
finding a match.

Issue: #22377

Modules/FindMatlab.cmake

@@ -1573,6 +1573,7 @@ if(_numbers_of_matlab_roots GREATER 0)
     list(GET _matlab_possible_roots ${_list_index} Matlab_VERSION_STRING)
     list(GET _matlab_possible_roots ${_matlab_root_dir_index} Matlab_ROOT_DIR)
   elseif(DEFINED Matlab_FIND_VERSION)
+    set(_list_index -1)
     foreach(_matlab_root_index RANGE 1 ${_numbers_of_matlab_roots} 3)
       list(GET _matlab_possible_roots ${_matlab_root_index} _matlab_root_version)
       if(_matlab_root_version VERSION_GREATER_EQUAL Matlab_FIND_VERSION)