patch 8.2.3083: crash when passing null string to charclass()

Problem:    Crash when passing null string to charclass().
Solution:   Bail out when string pointer is NULL. (Christian Brabandt,
            closes #8498, closes #8260)

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3083,
 /**/
     3082,
 /**/