idevice: Fix sign issue in idevice_get_device_list_extended

In sync with idevice_from_mux_device, line 384.
Without this fix, data size 128 (the common value) is treated as -128, resulting in incorrect allocation.
Related to #1248 but doesn't fully fix it.
diff --git a/src/idevice.c b/src/idevice.c
index adf47f4..22d57e3 100644
--- a/src/idevice.c
+++ b/src/idevice.c
@@ -284,7 +284,7 @@
 			newlist[newcount]->conn_data = NULL;
 		} else if (dev_list[i].conn_type == CONNECTION_TYPE_NETWORK) {
 			newlist[newcount]->conn_type = CONNECTION_NETWORK;
-			size_t addrlen = dev_list[i].conn_data[0];
+			size_t addrlen = ((uint8_t*)dev_list[i].conn_data)[0];
 			newlist[newcount]->conn_data = malloc(addrlen);
 			memcpy(newlist[newcount]->conn_data, dev_list[i].conn_data, addrlen);
 		}