False positive Uninitialized Value in C code

Version: v1.1.0

System: Debian Bullseye

Command:

```
infer --no-progress-bar -- cc \
auto_tests/auto_test_support.c \
auto_tests/lossless_packet_test.c \
testing/misc_tools.c \
toxav/*.c \
toxcore/*.c \
toxcore/*/*.c \
toxencryptsave/*.c \
third_party/cmp/*.c \
-lpthread \
$(pkg-config --cflags --libs libsodium opus vpx)
```

ran in the root directory of https://github.com/TokTok/c-toxcore repository.

Infer incorrectly reports Uninitialized Value:

```
Capturing in make/cc mode...
Found 79 source files to analyze in /root/work/infer-out

toxcore/Messenger.c:2734: error: Uninitialized Value
The value read from dht2m[_] was never initialized.
2732.
2733. for (uint32_t friend_idx = 0; friend_idx < num_dhtfriends; ++friend_idx) {
2734. const Friend *const msgfptr = dht2m[friend_idx] >= 0 ? &m->friendlist[dht2m[friend_idx]] : nullptr;
^
2735. const DHT_Friend *const dhtfptr = dht_get_friend(m->dht, friend_idx);
2736.

toxcore/Messenger.c:2739: error: Uninitialized Value
The value read from dht2m[_] was never initialized.
2737. if (msgfptr != nullptr) {
2738. char id_str[IDSTRING_LEN];
2739. LOGGER_TRACE(m->log, "F[%2u:%2u] <%s> %s",
^
2740. dht2m[friend_idx], friend_idx, msgfptr->name,
2741. id_to_string(msgfptr->real_pk, id_str, sizeof(id_str)));

toxcore/Messenger.c:2723: error: Uninitialized Value
The value read from m2dht[_] was never initialized.
2721.
2722. for (uint32_t friend_idx = 0; friend_idx < num_dhtfriends; ++friend_idx) {
2723. if (m2dht[friend_idx] >= 0) {
^
2724. assert(friend_idx < INT32_MAX);
2725. dht2m[m2dht[friend_idx]] = (int32_t)friend_idx;

toxcore/group_chats.c:6190: error: Dead Store
The value written to &ret (type int) is never used.
6188. }
6189.
6190. int ret = -1;
^
6191. const uint16_t payload_len = (uint16_t)len;
6192.

Found 4 issues
Issue Type(ISSUED_TYPE_ID): #
Uninitialized Value(UNINITIALIZED_VALUE): 3
Dead Store(DEAD_STORE): 1
```

Both `dht2m` and `m2dht` arrays are initialized to -1 in the loop right after their declaration:

https://github.com/TokTok/c-toxcore/blob/66453439acf79a35eb46fe66a1c72595e7d0c9ca/toxcore/Messenger.c#L2701-L2720

(Note that `break` breaks just the inner loop, the outer loop runs in its entirety, fully initializing the arrays).

`VAL` macro is defined in https://github.com/TokTok/c-toxcore/blob/66453439acf79a35eb46fe66a1c72595e7d0c9ca/toxcore/ccompat.h, expands to

```C
int32_t m2dht[num_dhtfriends];
int32_t dht2m[num_dhtfriends];
```

if you run `gcc -E` or `clang -E` on the code.