patch 9.1.1335: Coverity complains about Null pointer dereferences

Problem:  Coverity complains about Null pointer dereferences
Solution: before accessing ccline->cmdbuff check that ccline is not NULL

Fixes: Coverity issue 1646601
closes: #17189

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/cmdexpand.c b/src/cmdexpand.c
index 5b87d78..e8bc080 100644
--- a/src/cmdexpand.c
+++ b/src/cmdexpand.c
@@ -382,7 +382,7 @@
     }
 
     // Compute the popup menu starting column
-    compl_startcol = vim_strsize(ccline->cmdbuff) + 1;
+    compl_startcol = ccline == NULL ? 0 : vim_strsize(ccline->cmdbuff) + 1;
     columns = vim_strsize(xp->xp_pattern);
     if (showtail)
     {