patch 8.2.4901: NULL pointer access when using invalid pattern

Problem:    NULL pointer access when using invalid pattern.
Solution:   Check for failed regexp program.
diff --git a/src/version.c b/src/version.c
index ad38b81..647011a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4901,
+/**/
     4900,
 /**/
     4899,