patch 8.2.0544: memory leak in search test

Problem:    Memory leak in search test.
Solution:   Free msgbuf. (Dominique Pelle, closes #5912)
diff --git a/src/search.c b/src/search.c
index 95a27f8..e3265c2 100644
--- a/src/search.c
+++ b/src/search.c
@@ -1416,6 +1416,7 @@
 		// Reserve enough space for the search pattern + offset.
 		len = STRLEN(p) + off_len + 3;
 
+	    vim_free(msgbuf);
 	    msgbuf = alloc(len);
 	    if (msgbuf != NULL)
 	    {