bpo-33673: Install python-docs-theme even if Sphinx is already installed (GH-7163)

(cherry picked from commit 3d3e66c2daebd8e6b18944eac7546168c0006c78)

Co-authored-by: Andrés Delfino <adelfino@gmail.com>
diff --git a/Doc/make.bat b/Doc/make.bat
index c69cfae..3a4b365 100644
--- a/Doc/make.bat
+++ b/Doc/make.bat
@@ -13,7 +13,13 @@
     %PYTHON% -c "import sphinx" > nul 2> nul
     if errorlevel 1 (
         echo Installing sphinx with %PYTHON%
-        %PYTHON% -m pip install sphinx python-docs-theme
+        %PYTHON% -m pip install sphinx
+        if errorlevel 1 exit /B
+    )
+    %PYTHON% -c "import python_docs_theme" > nul 2> nul
+    if errorlevel 1 (
+        echo Installing python-docs-theme with %PYTHON%
+        %PYTHON% -m pip install python-docs-theme
         if errorlevel 1 exit /B
     )
     set SPHINXBUILD=%PYTHON% -c "import sphinx, sys; sys.argv[0] = 'sphinx-build'; sphinx.main()"