FindPython: Support for multiple searches in same directory

This is a complement to commit 9b0510fa57 (FindPython: add support for
multiple searches in same directory, 2025-01-05).

Modules/FindPython/Support.cmake

@@ -47,9 +47,10 @@ macro (_PYTHON_DISPLAY_FAILURE _PYTHON_MSG)
     endif ()
   endif()
 
+  set (${_PYTHON_BASE}_FOUND FALSE)
   set (${_PYTHON_PREFIX}_FOUND FALSE)
-  string (TOUPPER "${_PYTHON_PREFIX}" _${_PYTHON_PREFIX}_UPPER_PREFIX)
-  set (${_PYTHON_UPPER_PREFIX}_FOUND FALSE)
+  string (TOUPPER "${_PYTHON_BASE}" _${_PYTHON_BASE}_UPPER_PREFIX)
+  set (${_${_PYTHON_BASE}_UPPER_PREFIX}_FOUND FALSE)
 endmacro()