patch 9.0.0228: crash when pattern looks below the last line

Problem:    Crash when pattern looks below the last line.
Solution:   Consider invalid lines to be empty. (closes #10938)
diff --git a/src/regexp_nfa.c b/src/regexp_nfa.c
index 0dbc6b5..f8717f5 100644
--- a/src/regexp_nfa.c
+++ b/src/regexp_nfa.c
@@ -6774,10 +6774,16 @@
 			result = col > t->state->val * ts;
 		    }
 		    if (!result)
-			result = nfa_re_num_cmp(t->state->val, op,
-				(long_u)win_linetabsize(wp,
-						rex.reg_firstlnum + rex.lnum,
-						rex.line, col) + 1);
+		    {
+			linenr_T    lnum = rex.reg_firstlnum + rex.lnum;
+			long_u	    vcol = 0;
+
+			if (lnum > 0
+				   && lnum <= wp->w_buffer->b_ml.ml_line_count)
+			    vcol = (long_u)win_linetabsize(wp, lnum,
+								rex.line, col);
+			result = nfa_re_num_cmp(t->state->val, op, vcol + 1);
+		    }
 		    if (result)
 		    {
 			add_here = TRUE;