patch 8.1.0291: 'incsearch' highlighting not used for :sort

Problem:    'incsearch' highlighting not used for :sort.
Solution:   Handle pattern in :sort command.
diff --git a/src/ex_getln.c b/src/ex_getln.c
index d38fa4b..7928af7 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -316,6 +316,7 @@
 			&& (STRNCMP(cmd, "substitute", p - cmd) == 0
 			    || STRNCMP(cmd, "smagic", p - cmd) == 0
 			    || STRNCMP(cmd, "snomagic", MAX(p - cmd, 3)) == 0
+			    || STRNCMP(cmd, "sort", p - cmd) == 0
 			    || STRNCMP(cmd, "global", p - cmd) == 0
 			    || STRNCMP(cmd, "vglobal", p - cmd) == 0))
 		{
@@ -331,6 +332,16 @@
 			if (*skipwhite(p) == NUL)
 			    return FALSE;
 		    }
+
+		    // For ":sort" skip over flags.
+		    if (cmd[0] == 's' && cmd[1] == 'o')
+		    {
+			while (ASCII_ISALPHA(*(p = skipwhite(p))))
+			    ++p;
+			if (*p == NUL)
+			    return FALSE;
+		    }
+
 		    p = skipwhite(p);
 		    delim = *p++;
 		    end = skip_regexp(p, delim, p_magic, NULL);
@@ -359,7 +370,7 @@
 				search_last_line = ea.line2;
 			    }
 			}
-			else if (*cmd == 's')
+			else if (cmd[0] == 's' && cmd[1] != 'o')
 			{
 			    // :s defaults to the current line
 			    search_first_line = curwin->w_cursor.lnum;