libobs/util/dstr.c: Don't find/replace if empty

libobs/util/dstr.c

@@ -528,6 +528,9 @@ void dstr_replace(struct dstr *str, const char *find,
 	size_t find_len, replace_len;
 	char *temp;
 
+	if (dstr_isempty(str))
+		return;
+
 	if (!replace)
 		replace = "";