patch 8.2.4938: crash when matching buffer with invalid pattern

Problem:    Crash when matching buffer with invalid pattern.
Solution:   Check for NULL regprog.
diff --git a/src/version.c b/src/version.c
index 8cc9ceb..0a3a5df 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4938,
+/**/
     4937,
 /**/
     4936,