patch 8.2.0665: wrongly assuming Python executable is called "python"

Problem:    Wrongly assuming Python executable is called "python".
Solution:   Use detected python command. (Ken Takata, closes #6016)
            Also use CheckFunction if possible.

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    665,
 /**/
     664,
 /**/