TextSearch: fix passing search string to grep

Fix proposed by phoudoin.

Fixes #15650.

Change-Id: Ie7177aaa39ff593445506983cb0725b75ca7bc7d
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2149
Reviewed-by: Jérôme Duval <[email protected]>

src/apps/text_search/Grepper.cpp

@@ -271,6 +271,9 @@ Grepper::_RunnerThread()
 		argv[argc++] = "-i";
 	if (! fRegularExpression)
 		argv[argc++] = "-F";	 // no a regexp: force fixed string,
+	// Add double dash argument to tell grep
+	// it's the end of commands options
+	argv[argc++] = "--";
 	argv[argc++] = fPattern;
 	argv[argc] = NULL;