patch 8.2.4979: accessing freed memory when line is flushed

Problem:    Accessing freed memory when line is flushed.
Solution:   Make a copy of the pattern to search for.
diff --git a/src/window.c b/src/window.c
index fca0eea..984fb46 100644
--- a/src/window.c
+++ b/src/window.c
@@ -579,9 +579,16 @@
 		CHECK_CMDWIN;
 		if ((len = find_ident_under_cursor(&ptr, FIND_IDENT)) == 0)
 		    break;
+
+		// Make a copy, if the line was changed it will be freed.
+		ptr = vim_strnsave(ptr, len);
+		if (ptr == NULL)
+		    break;
+
 		find_pattern_in_path(ptr, 0, len, TRUE,
 			Prenum == 0 ? TRUE : FALSE, type,
 			Prenum1, ACTION_SPLIT, (linenr_T)1, (linenr_T)MAXLNUM);
+		vim_free(ptr);
 		curwin->w_set_curswant = TRUE;
 		break;
 #endif