BUG/MINOR: tools: Add OOM check for malloc() in indent_msg()

This patch adds a missing out-of-memory (OOM) check after
the call to `malloc()` in `indent_msg()`. If memory
allocation fails, the function returns NULL to prevent
undefined behavior.

Co-authored-by: Christian Norbert Menges <christian.norbert.menges@sap.com>

src/tools.c

@@ -4689,6 +4689,8 @@ char *indent_msg(char **out, int level)
 
 	needed = 1 + level * (lf + 1) + len + 1;
 	p = ret = malloc(needed);
+	if (unlikely(!ret))
+		return NULL;
 	in = *out;
 
 	/* skip initial LFs */