Fixes bitcoin#27472

Signed-off-by: Pttn <28868425+Pttn@users.noreply.github.com>

Github-Pull: bitcoin#27473
Rebased-From: 0d6383f

Compiling bdb with clang-16 on aarch64 (hardware) currently fails:
```bash
make -C depends/ bdb CC=clang CXX=clang++
...
checking for mutexes... UNIX/fcntl
configure: WARNING: NO SHARED LATCH IMPLEMENTATION FOUND FOR THIS PLATFORM.
configure: error: Unable to find a mutex implementation
```

Looking at config.log we've got:
```bash
configure:18704: checking for mutexes
configure:18815: clang -o conftest -pipe -std=c11 -O2 -Wno-error=implicit-function-declaration -Wno-error=format-security    -I/bitcoin/depends/aarch64-unknown-linux-gnu/include -D_GNU_SOURCE -D_REENTRANT   -L/bitcoin/depends/aarch64-unknown-linux-gnu/lib conftest.c  -lpthread >&5
conftest.c:45:1: error: type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int [-Wimplicit-int]
main() {
^
int
conftest.c:50:2: warning: call to undeclared library function 'exit' with type 'void (int) __attribute__((noreturn))'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
        exit (
        ^
conftest.c:50:2: note: include the header <stdlib.h> or explicitly provide a declaration for 'exit'
1 warning and 1 error generated.
```

Clang-16 changed `-Wimplicit-function-declaration` and `-Wimplicit-int`
warnings into errors, see:
https://releases.llvm.org/16.0.0/tools/clang/docs/ReleaseNotes.html#potentially-breaking-changes.

> The -Wimplicit-function-declaration and -Wimplicit-int warnings now
> default to an error in C99, C11, and C17. As of C2x, support for implicit
> function declarations and implicit int has been removed, and the
> warning options will have no effect. Specifying -Wimplicit-int in
> C89 mode will now issue warnings instead of being a noop.

Github-Pull: bitcoin#27462
Rebased-From: f8b8458

`evhttp_uri_parse` can return a nullptr, for example when the URI
contains invalid characters (e.g. "%").
`GetQueryParameterFromUri` passes the output of `evhttp_uri_parse`
straight into `evhttp_uri_get_query`, which means that anyone calling
a REST endpoint in which query parameters are used (e.g. `rest_headers`)
can cause a segfault.

This bugfix is designed to be minimal and without additional behaviour change.

Github-Pull: bitcoin#27468
Rebased-From: 11422cc