patch 8.1.0278: 'incsearch' highlighting does not accept reverse range

Problem:    'incsearch' highlighting does not accept reverse range.
Solution:   Swap the range when needed. (issue #3321)
diff --git a/src/ex_getln.c b/src/ex_getln.c
index a1cea9b..22f35e1 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -320,8 +320,17 @@
 			parse_cmd_address(&ea, &dummy);
 			if (ea.addr_count > 0)
 			{
-			    search_first_line = ea.line1;
-			    search_last_line = ea.line2;
+			    // Allow for reverse match.
+			    if (ea.line2 < ea.line1)
+			    {
+				search_first_line = ea.line2;
+				search_last_line = ea.line1;
+			    }
+			    else
+			    {
+				search_first_line = ea.line1;
+				search_last_line = ea.line2;
+			    }
 			}
 			else if (*cmd == 's')
 			{