net: coap: fix uninitialized usage of option struct

option struct was uninitialized in insert_option() function
during encode_options() call when the while loop wasn't
executed before.

Signed-off-by: Jakub Witowski <jakub.witowski9302@gmail.com>

Author: jakubwitowski

subsys/net/lib/coap/coap.c

@@ -1395,7 +1395,7 @@ int insert_option(struct coap_packet *cpkt, uint16_t code, const uint8_t *value,
 	uint16_t opt_len = 0;
 	uint16_t last_opt = 0;
 	uint16_t last_offset = cpkt->hdr_len;
-	struct coap_option option;
+	struct coap_option option = {0};
 	int r;
 
 	while (offset < cpkt->hdr_len + cpkt->opt_len) {